Cycle variation
Longer or shorter cycles may shift presumed ovulation, which is why cycle length is included in the calculation.
Everyday Tools · Family
Pregnancy Due Date Calculator
Estimate your baby's due date, current pregnancy week and trimester from your last menstrual period or conception date — using the same Naegele's Rule method doctors use as a starting estimate.
Your details
Due
Ledger
Ledger
Entry No. 01 — Estimated due date
—
estimated delivery date
Current pregnancy week—
Trimester—
Conception date (estimated)—
Days remaining—
This is an estimate for planning purposes. Confirm your due date with a gynaecologist and dating ultrasound.
Use the estimate safely
What can change an estimated due date?
A menstrual-period calculation assumes that the entered date and cycle pattern are reliable. Irregular cycles, uncertain period dates, recent hormonal contraception and differences in ovulation timing can shift the estimate. A conception-based calculation can also be uncertain unless conception timing is known accurately.
Early ultrasound
Clinical dating from an early scan may lead your healthcare professional to revise the initial estimate.
A due window
The estimated date is a planning reference, not a prediction that labour will begin on that exact day.
Use this calculator for general planning only. Prenatal appointments, symptoms and medical decisions should always be discussed with a qualified obstetric healthcare professional.
How it works
How to use the due date calculator
Choose your method
Pick "Last menstrual period" if you track your cycle, or "Conception date" if you know roughly when conception occurred.
Enter the date
Select the exact date from the calendar picker.
Adjust your cycle length
If your cycle isn't the average 28 days, entering your actual cycle length improves accuracy.
Read your results
See your estimated due date, current pregnancy week, trimester and days remaining.
Understanding due dates
How due dates are estimated
The standard method, known as Naegele's Rule, estimates a pregnancy to last 280 days (40 weeks) from the first day of your last menstrual period (LMP) — even though conception typically happens about two weeks after that date, near ovulation. If you instead know your conception date, doctors add 266 days (38 weeks) directly to that date.
Naegele's Rule assumes a textbook 28‑day cycle with ovulation on day 14. If your cycle runs longer or shorter than 28 days, the estimated ovulation — and therefore the due date — shifts accordingly. This calculator adjusts for that automatically.
| Trimester | Weeks |
|---|---|
| First trimester | Week 1 – Week 13 |
| Second trimester | Week 14 – Week 27 |
| Third trimester | Week 28 – Week 40+ |
Only around 5% of babies are born on their exact estimated due date — most arrive within a week or two of it. An early first‑trimester ultrasound generally gives the most accurate dating, and your doctor may revise the estimate based on it.
FAQ
Frequently asked questions
How is the due date calculated?
Naegele's Rule adds 280 days to the first day of your last menstrual period. If using a conception date instead, 266 days is added to that date.
How accurate is this calculator?
It's an estimate — only about 5% of babies arrive exactly on the calculated date. Most births happen within one to two weeks of it. A first‑trimester ultrasound is the most accurate dating method.
What if my cycle isn't 28 days?
The calculator adjusts the estimate based on the cycle length you enter, shifting the presumed ovulation day accordingly.
What are the three trimesters?
First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: week 28 through birth, typically around week 40.
Should I use this instead of my doctor's estimate?
No — this tool is for quick planning only. Always confirm your due date with a gynaecologist and dating ultrasound.
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