Pregnancy Due Date Calculator
Estimate a due date from the first day of the last menstrual period, adjusted for cycle length.
- Estimated conceptionAug 7, 2026
- Estimated due dateApr 30, 2027
Inputs used
- First day of last periodJul 24, 2026
- Average cycle length28 days
About this calculator
The standard estimate (Naegele's rule) puts the due date 280 days — 40 weeks — after the first day of the last menstrual period. That assumes a 28-day cycle with ovulation on day 14, so the calculator shifts the estimate by one day for each day your average cycle differs from 28.
It is genuinely an estimate: only about 1 in 20 babies arrives on the calculated date, and most are born within a two-week window either side. An early ultrasound gives a more accurate date and is what clinicians go by when the two disagree.
This calculator is for general information — confirm dates and plan care with your midwife or doctor.
Frequently asked questions
How is a due date calculated?
The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period. This calculator then shifts the estimate by one day for each day your average cycle differs from 28, since a longer or shorter cycle moves ovulation.
How accurate is an estimated due date?
It is genuinely an estimate: only about 1 in 20 babies arrives on the calculated date, and most are born within roughly two weeks either side. An early ultrasound gives a more accurate date and is what clinicians rely on when the two disagree.
What if my cycle isn't 28 days?
Naegele's rule assumes a 28-day cycle with ovulation on day 14, so this calculator adjusts by the difference: a 32-day cycle pushes the due date about four days later, and a 25-day cycle brings it about three days earlier.
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Results are informational only — not financial, medical or legal advice.