How accurate is the calculator?

It gives an estimated due date (EDD). Only about 5% of babies are born exactly on their due date — most arrive within 2 weeks either side.

Pregnancy is divided into 3 trimesters: 1st (weeks 1–12), 2nd (weeks 13–26), 3rd (weeks 27–40).

Why is pregnancy dated from my last period instead of conception?

Naegele's Rule dates from the LMP because it's the most reliably known date for most people — conception typically happens about 2 weeks later, which is already built into the 280-day calculation.

Can an ultrasound change my due date?

Yes — an early ultrasound (typically weeks 8-13) often gives a more accurate estimate than LMP-based dating alone, especially if your cycle isn't a standard 28 days. Your doctor may adjust the date after your first scan.

Pregnancy Due Date Calculator

Calculate your pregnancy due date from last menstrual period, conception date, or IVF transfer date. Shows current week, trimester, and key milestones.

Calculation method

Last Period (LMP) date

How to Use

1
Choose calculation method
Select Last Period (LMP), Conception date, or IVF transfer date depending on what you know.
2
Enter the date
Pick the relevant date from the date picker.
3
View your due date
See your estimated due date, current week, trimester, progress percentage, and key milestones.

How It Works

This calculator estimates your due date using the same methods obstetricians use — Naegele's Rule from your last menstrual period, or a direct offset from a known conception or IVF transfer date — and shows your current week, trimester, and progress.

Naegele's Rule (from Last Menstrual Period)

Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14 — pregnancy is conventionally dated from the LMP even though conception happens about two weeks later, which is why "40 weeks pregnant" doesn't mean 40 weeks since conception.

From a known conception or IVF date

If you know your conception date, the due date is conception + 266 days (38 weeks), since this skips the ~14-day gap between LMP and ovulation already built into Naegele's Rule. For IVF, the due date is calculated from the transfer date plus the known embryo age at transfer (e.g. a day-5 blastocyst transfer + 261 days) — generally the most precise of the three methods since the exact fertilization timing is known.

Examples

LMP-based estimate

If your last period started on 1 January, adding 280 days gives an estimated due date of 8 October — with the current trimester and week-by-week progress shown based on today's date.

IVF transfer-based estimate

For a day-5 blastocyst transferred on 1 March, the due date is 1 March + 261 days ≈ 16 November — typically more precise than LMP dating since the embryo's exact age is known at transfer.

Common Use Cases

Getting an early estimated due date to plan leave, appointments, and preparations
Tracking which trimester and week you're currently in
Cross-checking a due date given by LMP against a known conception or IVF date
Understanding pregnancy milestones tied to specific weeks (e.g. end of first trimester at week 12)

Tips

Only about 5% of babies are born exactly on their estimated due date — most arrive within about two weeks before or after, so treat the date as a planning target, not a prediction.
An early ultrasound (typically 8–13 weeks) often provides a more accurate due date than LMP-based dating alone, especially if your cycle isn't a standard 28 days — your doctor may adjust the date after your first scan.
The three trimesters are conventionally weeks 1–12, 13–26, and 27–40 — but exact boundaries can vary slightly by source, so don't be surprised by minor differences between calculators or care providers.

Frequently Asked Questions

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