Due date calculator
An estimated due date from your last period, adjusted for your cycle length.
- Runs in your browser — nothing you enter is uploaded
- No sign-up, no quotas, free to use as often as you like
How it works
The standard estimate counts 280 days from the first day of your last period. That assumes a 28-day cycle, which is where the common version of this calculation loses accuracy — so this one adjusts for the cycle length you actually have.
How it is calculated
Naegele's rule: 280 days from the first day of the last period. If your cycle is longer or shorter than 28 days, ovulation happens correspondingly later or earlier, so the estimate is shifted by the difference. A 35-day cycle moves the date a week later than the unadjusted rule would suggest.
How far along, and which trimester
If your last period was recent enough, the tool also shows how far along you are today in weeks and days — the format used in maternity care — along with the trimester and the days remaining.
How approximate this is
Very. Only about one birth in twenty happens on the estimated date, and a normal term spans several weeks around it. Cycle length varies month to month, ovulation timing varies within a cycle, and the date of the last period is often remembered approximately. A dating scan is considerably more accurate than any calculation from a calendar, which is why maternity services use one.
Not medical advice
This is a calendar calculation and nothing more. It does not confirm a pregnancy, assess one, or replace anything a midwife or doctor does.
Due date calculator — questions
How accurate is the due date?
It is an estimate. Only about 5% of births happen on the date itself, and a normal term covers several weeks around it.
What if my cycle is not 28 days?
Enter your usual length and the estimate is adjusted, which is the main thing that makes this more accurate than the plain rule.
What if I do not know my last period date?
Then this calculation cannot be done reliably. A dating scan is the accurate route and is what maternity services use.
Does it work from a conception date?
Not directly. Conception is roughly two weeks after the start of the last period, so you can work backwards, but the estimate is defined from the period date.
Is this medical advice?
No. It is a calendar calculation, and no substitute for a midwife or doctor.