Pregnancy Due Date Calculator — Free EDD Tool

One of the first questions after a positive pregnancy test is: “When is the baby due?” The standard medical answer comes from Naegele’s rule — add 280 days (40 weeks) to the first day of your last menstrual period — and it is the same method most doctors and midwives use for the initial estimate.

Our free pregnancy due date calculator applies Naegele’s rule instantly. Enter the first day of your last period and you get your estimated due date, how many weeks and days pregnant you are right now, your current trimester, days remaining, and a full table of milestone dates from estimated conception through the end of each trimester to full term.

These are estimates for planning and excitement — your healthcare provider will confirm or adjust the date with an early ultrasound. The tool is free, private and requires no sign-up.

How to use the pregnancy due date calculator

1. Enter the first day of your last period. Not the day it ended — the day bleeding started.
2. Check your due date. Calculated as last period + 280 days, shown with the weekday.
3. See how far along you are. Weeks and days of pregnancy as of today, plus your trimester.
4. Review the milestones. Estimated conception date, end of each trimester, the 24-week viability milestone and the 37-week full-term mark.
5. Count down. The days-remaining figure tells you exactly how long until the big day.
6. Confirm with your provider. Bring the estimate to your first prenatal visit for ultrasound confirmation.

Key features & benefits

• Naegele’s rule math. The same 280-day method clinicians use for the initial due date estimate.
• Current progress. Weeks + days pregnant today, so you always know exactly where you are.
• Trimester indicator. Instantly shows whether you are in the first, second or third trimester.
• Six milestone dates. Conception estimate, trimester boundaries, viability and full-term dates in one table.
• Live countdown. Days remaining until the due date, updating automatically each day.
• Private and free. Sensitive dates stay in your browser — nothing is uploaded or stored.
• No sign-up. One date input, instant answers, on any device.

How Naegele’s rule works

Naegele’s rule assumes a 28-day cycle with ovulation on day 14: due date = first day of last period + 7 days − 3 months + 1 year, which equals 280 days. If your cycles are consistently longer or shorter, ovulation shifts and the estimate shifts with it — mention your typical cycle length to your provider. An early ultrasound (before 14 weeks) gives the most accurate dating and may adjust this estimate by a few days.

What the milestones mean

The first trimester ends around 13 weeks 6 days, the second around 27 weeks 6 days. Twenty-four weeks is the commonly cited viability milestone, and 37 weeks marks full term — though only about 5% of babies arrive exactly on their due date, with most coming within two weeks either side. Planning other date math? The date duration calculator measures time between any two dates, and the age calculator computes exact ages.

Want a live ticking countdown to the big day? Set one with the countdown timer, or check which ISO week your due date lands in with the week number finder.

Frequently asked questions

How It Works: Under the Hood

The standard method is Naegele’s rule: add 7 days to the first day of the last menstrual period (LMP), subtract 3 months, add 1 year — equivalent to LMP + 280 days (40 weeks). This assumes a textbook 28-day cycle with ovulation on day 14. The calculator also derives the current gestational age (today − LMP), the trimester (weeks 1–12, 13–27, 28–40), and the estimated conception date (LMP + 14 days).

For irregular cycles, the math shifts: ovulation typically occurs ~14 days before the next period, not 14 days after the last one. A 35-day cycle means ovulation around day 21, so the due date moves a week later than Naegele’s rule gives. Good calculators adjust for cycle length rather than blindly assuming 28 days.

Important context: the “40 weeks” counts from LMP, not conception — so at a positive test (~4 weeks pregnant), the embryo is really ~2 weeks old. And only about 5% of babies arrive on the due date; the medically normal window is 37–42 weeks. The date is a planning anchor, not an appointment.

Real-World Use Cases

• First-trimester planning: a newly pregnant woman calculates her due date the day of the positive test, then works backward to schedule the 8-week first prenatal appointment and the 12-week screening window.
• Work leave planning: a couple uses the due date plus the 37–42 week window to discuss maternity/paternity leave timing with employers months in advance.
• Tracking milestones: parents follow week-by-week development guides (“week 20: anatomy scan”) — all indexed to gestational age, which starts from this calculation.
• IVF pregnancies: for embryo transfers, dating uses the transfer date minus/plus fixed offsets (day-3 transfer = LMP equivalent 17 days earlier; day-5 blastocyst = 19 days) — more precise than LMP-based dating.
• Healthcare handoffs: a woman switching OB practices mid-pregnancy brings her LMP-derived dates so the new provider’s ultrasound dating has a baseline to confirm against.

Advanced Tips

• Enter the first day of LMP, not the last: the most common input error. The calculation anchors to day 1 of bleeding — entering the end of the period shifts everything by nearly a week.
• Adjust for cycle length honestly: if your cycles are consistently 32 days, say so. The 28-day default exists for the textbook case; real bodies vary, and the adjustment meaningfully changes the date.
• Know when ultrasound overrides LMP: a first-trimester ultrasound (crown-rump length) dates pregnancy to ±5 days — more accurate than LMP math. If they disagree by more than a week, clinicians go with the ultrasound.
• Count in weeks + days: clinicians say “24w3d”, not “about 6 months”. Tracking the exact week-day format keeps you aligned with every medical chart and milestone guide you’ll encounter.

Common Mistakes to Avoid

• Treating the due date as a deadline: going “overdue” to 41 weeks is medically normal. Panicking at 40w1d — or scheduling life rigidly around the exact date — creates unnecessary stress.
• Using conception date as LMP: if you know the exact conception day, add 266 days (38 weeks), not 280. Mixing the two baselines is the classic home-calculation error.
• Ignoring irregular cycles: with PCOS or postpartum irregular cycles, LMP math can be off by weeks. In these cases the calculator gives a rough estimate only — early ultrasound dating is essential.
• Forgetting it’s an estimate for planning, not diagnosis: this tool doesn’t replace prenatal care. Dating affects screening windows and growth assessments — confirm everything with your healthcare provider.

Planning Around the Milestones, Not Just the Date

The due date gets all the attention, but the milestone table is the practical part. The 24-week viability mark and the 37-week full-term mark bracket the window when preparations shift from relaxed to urgent; trimester boundaries tell you when screening appointments and classes typically fall. Use the days-remaining countdown to pace nursery setup, parental-leave paperwork, and travel plans — counting backward from milestones beats counting forward from today. When you need the gap between two appointments, the date duration calculator measures it precisely.

Why Only About 4% Arrive on the Date

An estimated due date is a planning anchor, not an appointment — first babies especially tend to arrive after it. That is normal, not a miscalculation: Naegele’s rule assumes a textbook 28-day cycle, and real cycles vary. Your provider’s early ultrasound may shift the date by days, which is a refinement, not a contradiction. Treat the estimate as the center of a two-week window on either side. After the arrival, track the little one’s growth milestones with the age calculator.