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Pregnancy Due Date Calculator

Educational use only — not medical advice. Read the full disclaimer.

Enter the first day of your last period and your average cycle length to estimate your due date, current gestational age, trimester, ovulation window, and key pregnancy milestones.

  • Trusted method (Naegele’s Rule)
  • Cycle length adjustment
  • Ovulation & fertile window
  • Milestone timeline

Reviewed: January 27, 2026 — Reviewed for due‑date math, cycle adjustments, and plain‑language safety notes.

Calculate your due date

How the calculator works (and what it means)

We apply Naegele’s Rule (40 weeks from the first day of your last period) and adjust for your cycle length. The result is an estimate: most babies arrive between 37–41 weeks. An early ultrasound (8–12 weeks) is often used by providers to refine dates.

Appointment timeline (typical)

  • 8–12 weeks: Dating/viability ultrasound; initial labs.
  • 12–14 weeks: NT scan (optional depending on region); screening choices.
  • 18–22 weeks: Anatomy scan (detailed fetal survey).
  • 24–28 weeks: Glucose screening, anemia check.
  • 28 weeks: Third trimester begins; Tdap timing varies by region.
  • 36–40 weeks: Group B strep screening; weekly visits may begin.

Next steps by trimester

First trimester

  • Start/continue prenatal vitamins (folate, iron as advised).
  • Discuss nausea strategies and safe medication questions with your provider.
  • Consider genetic screening options if offered.

Second trimester

  • Schedule anatomy scan and review results with your provider.
  • Plan glucose screening; track fetal movement trends later in the trimester.
  • Explore childbirth classes and birth preferences.

Third trimester

  • Pack a hospital bag; confirm support plans.
  • Review kick-count guidance and signs to call your provider.
  • Discuss induction policies around 41–42 weeks if pregnancy continues.

Clear logic

Transparent math with cycle adjustments and milestone mapping.

Privacy-first

No accounts. No saved data. Your inputs stay in your browser.

Helpful guides

Five in-depth blogs to answer common questions and next steps.

Quick glossary

LMP

Last Menstrual Period — the first day of your last period; used as the starting point for dating.

EDD

Estimated Due Date — 40 weeks from LMP (adjusted by cycle length) or set by early ultrasound.

GA

Gestational Age — how far along the pregnancy is, counted from LMP (in weeks and days).

NT / NIPT

Nuchal translucency measurement and noninvasive prenatal testing — optional screening approaches.

When to call your provider

The following are general signs to seek medical guidance right away. When in doubt, call your provider or local emergency number.

  • Heavy bleeding, severe abdominal pain, or persistent vomiting
  • Fever, chills, or signs of dehydration
  • Severe headache, vision changes, or sudden swelling
  • Noticeable decrease in fetal movement after you’ve been feeling regular movement

Reminder: This site is educational only and does not replace professional medical advice.

Irregular cycles & special cases

  • If your cycles vary widely, use your best average for now and plan to compare with an early ultrasound.
  • Conceived via IVF or assisted reproduction? Use your clinic’s dates; transfer day and embryo age change the math.
  • Recently stopped hormonal birth control? Cycles can shift temporarily; early ultrasound helps.
Read: How cycle length affects your due date →

Save, print, or share your results

After you calculate, use the buttons below to print or copy a link with your inputs.

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How we estimate your due date

We start with Naegele’s rule (LMP + 280 days ≈ 40 weeks) and let you adjust for your average cycle length. Irregular cycles, late ovulation, IVF transfer dates, or a first-trimester ultrasound can shift dates. Your clinician’s assessment always overrides this calculator.

  • Regular cycles (28 days): LMP + 280 days
  • Longer/shorter cycles: add/subtract the difference from 28 days
  • Ultrasound dating: first-trimester CRL often provides the most accurate EDD
  • IVF: use retrieval or 3/5-day transfer date for baseline
  • Multiples (twins+): average gestation can differ from singletons

This is an educational estimate. If your results differ from your care team’s, follow their guidance.

What your estimated due date means

Pregnancy length is measured in weeks from the first day of your last menstrual period (LMP). Your estimated due date (EDD) marks the completion of 40 weeks—only about 5% of births occur exactly on that day.

Most people deliver sometime during the two weeks before or after the EDD. Your care team uses the EDD to plan visits, screening windows, and discussions about birth preferences.

  • First trimester: 0–13 weeks — early development and first ultrasound dating
  • Second trimester: 14–27 weeks — anatomy scan and feeling fetal movement
  • Third trimester: 28–40+ weeks — growth monitoring and preparing for delivery

Your clinician may adjust the EDD if ultrasound measurements suggest a more accurate date.

How accurate is a due date?

Due dates are estimates because ovulation and implantation vary. A first‑trimester ultrasound (crown‑rump length) usually offers the smallest margin of error.

Later in pregnancy, babies grow at different rates, so second‑ and third‑trimester ultrasounds are less precise for dating than early scans.

  • LMP + typical 28‑day cycle: common starting point
  • Cycle‑length adjustment: longer cycles often push EDD later; shorter cycles bring it earlier
  • First‑trimester ultrasound: often the best single source for establishing EDD
  • IVF pregnancies: dating uses retrieval or embryo transfer date (3- or 5‑day transfer)

Cycle length matters

If your average cycle isn’t 28 days, the calculator adjusts the baseline. For example, with a 32‑day cycle, ovulation may occur about four days later than the 14‑day norm—so the EDD typically shifts later as well.

If your cycles are irregular, your clinician may rely more on ultrasound findings to set the official EDD.

  • Longer cycles (e.g., 32 days): EDD often shifts later
  • Shorter cycles (e.g., 25 days): EDD often shifts earlier
  • Irregular cycles: ultrasound dating may override LMP‑based estimates

When to contact your clinician

Always reach out to a qualified professional with questions about your pregnancy or if something feels off. This calculator cannot evaluate symptoms or risks.

  • Severe abdominal pain, heavy bleeding, or fluid leakage
  • Fever, severe headache, vision changes, or sudden swelling
  • Decreased fetal movement in the third trimester
  • Any symptoms that worry you

In an emergency, call your local emergency number (e.g., 911 in the U.S.) or go to the nearest emergency department.

Next steps after you get an estimate

Save or print your result and compare it with your care team’s date at your next visit. Use the EDD to plan routine appointments, prenatal vitamins, and maternity leave timing where applicable.

  • Add upcoming prenatal visit windows to your calendar
  • Read your clinic’s guidance on screening and vaccines
  • Start a list of questions for your next appointment
  • Bookmark this page to re‑check dates if your cycle data changes

Important reminder

This tool is for education only and can’t replace personalized medical advice. Your clinician’s assessment—especially when based on early ultrasound—should guide decisions.

Why due dates are ranges, not exact deadlines

Even with perfect dating, birth timing varies. Many births happen in the weeks around the estimated due date. Your care team uses the EDD to plan the timing of labs, ultrasounds, and routine visits—not to predict the exact day labor starts.

Common reasons dates shift

  • Ovulation timing: not everyone ovulates on day 14.
  • Cycle variability: shorter or longer cycles can move the estimate.
  • Uncertain LMP: spotting can be confused with a true period.
  • Ultrasound confirmation: early measurements may refine the “official” EDD.

For clinician-focused guidance on establishing the EDD, see the professional references linked in our Editorial Standards.

What to do with your result

  • Save the EDD and gestational age to discuss at your next appointment.
  • If you have an ultrasound date from early pregnancy, compare the two and follow your clinic’s selected EDD.
  • Use the milestone list as a planning guide (screening windows, trimester changes, and basic prep).

Important: if anything feels urgent—severe pain, heavy bleeding, fever, fluid leakage—contact a qualified clinician or emergency services.

Make the estimate more useful in real life

An estimated due date is most helpful when you pair it with a few details that clinicians actually use during scheduling: your typical cycle pattern, any known ovulation timing, and whether you had fertility treatment or an early scan. The goal is simple: arrive at one “official” EDD that your care team uses for every appointment window.

What to bring to your first prenatal visit

  • A note of your last menstrual period start date and how sure you are about it (certain, pretty sure, unsure).
  • Your typical cycle range (for example: “26–30 days” rather than a single number).
  • Any positive test dates and whether they were faint/strong (helpful context, not diagnostic).
  • Medication/supplement list (include dose and how often).
  • Any prior pregnancy or surgery history you want documented.

Tip: if you track cycles in an app, a screenshot of the last 2–3 months can save time.

Mini‑glossary for dating terms

  • LMP: first day of the last menstrual period (the most common starting point for “weeks pregnant”).
  • GA: gestational age, counted from LMP (typically ~2 weeks ahead of conception timing).
  • EDD: estimated due date, the 40‑week mark used for planning—not a promise.
  • CRL: crown‑rump length measurement used early in pregnancy to estimate dating.
  • Fetal age: an informal term closer to conception timing; not used for most scheduling.

If any of these terms show up on your ultrasound report, you’ll know what they’re referring to.

Why your EDD can change (and why that’s normal)

Two people can enter the same LMP but end up with different clinic‑chosen due dates because providers prioritize consistency for screening windows. If an early scan strongly disagrees with an LMP estimate, clinics often “redate” so that growth checks and tests land in the right week.

  • Late ovulation: common with longer cycles; can push the EDD later than an LMP‑only estimate.
  • Uncertain LMP: missed or irregular bleeding can make LMP less reliable than ultrasound.
  • Fertility treatment: transfer/retrieval dates can anchor dating more precisely than a cycle estimate.
  • Multiple gestation: the due date may be set similarly, but delivery planning differs.

Bottom line: once your clinic selects an EDD, use that date everywhere (appointments, leave planning, baby registry checklists). It reduces confusion.

How to use this calculator like a pro

A due date estimate is most helpful when you treat it as a planning tool. Use it to organize questions for appointments, understand which week you’re in, and map out common milestones.

Start with your best-known reference: the first day of your last menstrual period (LMP). Then refine with your average cycle length if you don’t typically ovulate on day 14.

If you have an early ultrasound date or IVF transfer date, compare it to the estimate here and follow the date your care team confirms.

  • Pick one “official” date: once your clinic confirms an EDD, use that everywhere (apps, calendars, paperwork).
  • Track week-by-week: save your gestational age for future reference instead of recalculating from scratch.
  • Use notes, not guesses: write down cycle length, irregularities, and any known ovulation signs for your next visit.

Calendar-friendly milestones you can plan around

Many people like to plan the next few steps immediately after getting an estimate. The items below are intentionally general so they can fit different clinics and personal situations.

Your exact schedule may differ, but having a rough roadmap reduces stress and helps you ask better questions.

  • Early confirmation: initial visit timing varies; ask when your clinic prefers the first in‑person appointment.
  • Screening conversations: genetic screening options are time‑sensitive—ask what windows your clinic uses.
  • Anatomy scan planning: many providers schedule the anatomy scan in the mid‑pregnancy range.
  • Third‑trimester prep: discuss birth preferences, hospital registration, and pediatrician selection before things get hectic.

Common reasons your date may change

Seeing a different number in another app can be frustrating. In practice, small shifts usually come from assumptions each tool makes about ovulation or cycle length.

Clinicians often rely on early measurements if they better match fetal development, especially when cycles are irregular.

  • Irregular cycles: LMP isn’t a great anchor when timing varies month to month.
  • Late ovulation: a longer follicular phase can push dates later than a 28‑day model.
  • Early ultrasound: measurements early in pregnancy can align more closely with actual development than calendar math.
  • IVF dating: retrieval or transfer dates provide a clearer baseline than LMP.

How to interpret your due date estimate

Below is a more detailed, step‑by‑step explanation designed to answer the common “why did my date change?” questions. We summarize the key variables that influence an estimated due date (EDD), including last menstrual period timing, average cycle length, and whether you have an early ultrasound date.

Three dates you’ll hear

  • LMP: first day of your last period (calendar date)
  • Gestational age: weeks pregnant based on dating method
  • EDD: the estimated due date used for planning windows

Why estimates can differ

  • Ovulation doesn’t always occur on day 14
  • Implantation timing varies by a few days
  • Early ultrasound may refine the baseline

Quick reality check

It’s normal for your estimate to shift by a few days when you add cycle data or compare to a first‑trimester scan. Small adjustments are common; bigger shifts are a reason to ask your clinic which dating method they are using and why.

What to do with the result

Save your dates, then use them to plan routine prenatal milestones (screening windows, anatomy scan range, glucose screening timing, and leave planning). Bring the printed result to your next appointment so your care team can confirm the official date in your chart.

More context for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation)

When your care plan differs from an estimate, your clinician’s assessment should lead. It’s written to help you understand the logic and the planning implications without turning the page into medical advice. This section adds extra, page-specific guidance for **Pregnancy Due Date Calculator (EDD, Trimester & Ovulation)** so the content stands on its own for visitors coming from search. This is especially relevant for readers using the “index” resource.

A good way to use this page is to read once, then return later with your own dates and notes so you can spot what changed. Small inputs can shift the output by days—so clarity matters more than perfection. If you’re tracking multiple sources (app, clinic portal, ultrasound notes), label each date with where it came from and when it was recorded. If you’re here from the “index” page, use this as your quick reference.

Use this page to organize information, not to replace individualized care. Below you’ll find a checklist you can personalize and a short set of appointment questions to keep your next visit efficient. If anything feels urgent or symptom-related, it’s safer to contact a professional than to troubleshoot online. If you’re here from the “index” page, use this as your quick reference.

Personal planning checklist

  • Planning windows for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation): Add the next key planning windows to your calendar (appointments, screening windows, travel, work deadlines). (reference: index).
  • Cycle pattern for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation): Summarize your recent cycle pattern (typical range, any late ovulation clues, and any schedule disruptions). (reference: index).
  • Date inputs for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation): Record the exact date source you used (LMP, transfer, retrieval, or ultrasound) and note which one your clinic considers official. (reference: index).
  • Symptoms log for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation): Jot down changes since your last visit (sleep, nausea pattern, appetite, energy, mood) so you can describe trends instead of single days. (reference: index).
  • Meds & supplements for Pregnancy Due Date Calculator (EDD, Trimester & Ovulation): List meds/supplements with dosage and timing so your clinician can quickly review what you’re taking. (reference: index).

Appointment questions you can reuse

  • For readers using index: Which dating method are you using as the primary anchor in my chart, and why is it preferred for my situation?
  • For readers using index: Can we confirm the next appointment plan and what I should track between now and then?
  • For readers using index: Are there activity, travel, or work adjustments you recommend based on my history and current findings?
  • For readers using index: What are the next time-sensitive milestones for me, and what happens if a screening window is missed or delayed?

If you want to save your result, take a screenshot and note your input assumptions next to it—this prevents confusion later. When you compare estimates, compare the inputs first; most disagreements come from different baseline dates, not from “wrong math.” If your clinician updates your due date after an early ultrasound, treat that as the new planning anchor. This is especially relevant for readers using the “index” resource.

More helpful information

This page includes additional practical notes tailored to “Pregnancy Due Date Calculator (EDD, Trimester & Ovulation)” to help you use the information here with confidence. Last expanded on 2026-01-27.

How to use this page

Planning tip: after you get an estimate, save a screenshot. Then map out trimester windows for visits, screening, and personal planning (work, travel, and support). If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 26-day cycle. When ovulation is later, the estimated due date often shifts later too.

If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 28-day cycle. When ovulation is later, the estimated due date often shifts later too. Early pregnancy dates are usually most reliable when confirmed in the first trimester. If your first‑trimester scan gives a different date than LMP, your clinician may use the ultrasound date as the baseline.

If you conceived with fertility treatment (like IVF), dating is usually anchored to retrieval or transfer timing rather than LMP. Your clinic can give the most precise baseline. If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 25-day cycle. When ovulation is later, the estimated due date often shifts later too.

Planning tip: after you get an estimate, add it to your calendar. Then map out trimester windows for visits, screening, and personal planning (work, travel, and support). For planning, think in windows rather than one exact day. Many births happen within ~2 weeks of the estimated due date, and schedules (labs, scans) are built around that. If you conceived with fertility treatment (like IVF), dating is usually anchored to retrieval or transfer timing rather than LMP. Your clinic can give the most precise baseline.

  • Note your LMP, usual cycle length, first positive test date, and any scan date—having them handy helps conversations with your clinician (82f800).
  • Use your due date as a planning window (not a promise). Your care team’s dating guidance is the official source (eacf33).
  • When estimates disagree, your clinician can explain which source is considered “official” for you and why (d760bf).

Questions and next steps

Bring your estimate to your midwife visit along with any cycle notes (average length, first positive test date, and any tracking app data). That context helps your team choose the best official dating method. Early pregnancy dates are usually most reliable when confirmed in the first trimester. If your dating ultrasound gives a different date than LMP, your clinician may use the ultrasound date as the baseline. If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 28-day cycle. When ovulation is later, the estimated due date often shifts later too.

If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 27-day cycle. When ovulation is later, the estimated due date often shifts later too. Planning tip: after you get an estimate, print the result. Then map out trimester windows for visits, screening, and personal planning (work, travel, and support). Early pregnancy dates are usually most reliable when confirmed in the first trimester. If your dating ultrasound gives a different date than LMP, your clinician may use the ultrasound date as the baseline.

Bring your estimate to your care team visit along with any cycle notes (average length, first positive test date, and any tracking app data). That context helps your team choose the best official dating method. If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 29-day cycle. When ovulation is later, the estimated due date often shifts later too. Planning tip: after you get an estimate, print the result. Then map out trimester windows for visits, screening, and personal planning (work, travel, and support).

If you’re using an LMP-based estimate, remember it assumes ovulation around day 14 of a 26-day cycle. When ovulation is later, the estimated due date often shifts later too. Early pregnancy dates are usually most reliable when confirmed in the first trimester. If your first‑trimester scan gives a different date than LMP, your clinician may use the ultrasound date as the baseline. If you conceived with fertility treatment (like IVF), dating is usually anchored to retrieval or transfer timing rather than LMP. Your clinic can give the most precise baseline.

  • Bring a mini question list (3–5 items) to your next visit so you leave with clear answers (b30690).
  • Revisit this estimate if you change your cycle-length input or receive new dating information from an ultrasound or IVF timeline (1785ff).
  • Get urgent medical help for heavy bleeding, severe pain, fainting, or any symptom that feels alarming—trust your instincts (aab9f2).

Reminder for “Pregnancy Due Date Calculator (EDD, Trimester & Ovulation)”: this content is educational and should not replace professional medical advice.

Trust checklist for using any due‑date estimate

  1. Confirm your starting point. Use the first day of your last menstrual period (LMP) unless your clinician tells you to use a different reference.
  2. Tell your clinic about cycle patterns. Longer/shorter or irregular cycles can shift dates, screening windows, and interpretation.
  3. Prefer early dating when available. If an early ultrasound is performed, many clinics use it to set or confirm the official EDD.
  4. Write down discrepancies. If your result differs from your visit summary, bring both numbers to your next appointment.
  5. Plan with ranges, not a single day. Use the EDD to guide a “due‑date window,” not a guaranteed delivery date.

We keep the calculator simple on purpose: it provides an educational estimate and helps you organize questions for your clinician.