Pregnancy Due Date Calculator
Instant results as you type.
days
Estimated due date
2027-02-05
How far along13 weeks 5 days
TrimesterSecond
Days to go184
What this meansEstimated due date 2027-02-05, from Naegele's rule of 280 days after the last period. It is a median, not an appointment: fewer than one in twenty babies arrive on the estimated date, and anything from 37 to 42 weeks is full term. A dating scan is more accurate than any formula.
For education only — this is not medical advice. The figures are population averages: real energy use, appetite and rate of loss vary from person to person, and weight loss slows as you get lighter. If you are pregnant, managing diabetes, heart or joint conditions, or taking medication, talk to a doctor before changing your diet or activity.
A due date is calculated from the first day of the last period using Naegele's rule — 280 days, adjusted here if your cycle is not 28 days, since ovulation shifts with cycle length. It is worth understanding what the date is: a median, not an appointment. Fewer than one in twenty babies arrive on it, and anything from 37 to 42 weeks is full term.
How to use it
- Enter the first day of your last menstrual period.
- Enter your usual cycle length if it is not 28 days.
- Read the estimated due date, how far along you are, and the trimester.
Examples
- A last period starting 1 May 2026 with a 28-day cycle gives 5 February 2027.
- The same date with a 35-day cycle gives 12 February — a week later.
Frequently asked questions
- How is a due date calculated?
- Naegele's rule adds 280 days — forty weeks — to the first day of the last menstrual period. It assumes a 28-day cycle with ovulation on day 14, so this calculator adjusts when you enter a different cycle length. Note that dating from the last period means the first two weeks of a pregnancy predate conception.
- How accurate is an estimated due date?
- As a single date, not very — under 5 per cent of babies are born on it. As a centre point it is reliable: most births fall within two weeks either side, and 37 to 42 weeks is considered full term. Treat it as the middle of a window rather than a deadline.
- What if my cycle is not 28 days?
- Then the standard rule is off by the difference, because ovulation happens roughly 14 days before the next period rather than 14 days after the last. A 35-day cycle pushes the estimate about a week later, which this calculator applies. Very irregular cycles make period-based dating unreliable, and a scan is the better basis.
- Is a dating scan more accurate than this?
- Yes, particularly in the first trimester, where measuring the embryo dates a pregnancy to within a few days. Clinicians routinely revise a period-based date when an early scan disagrees materially. Use this calculator for orientation, and let the scan set the date that goes in your notes.