Due date calculator
Three ways to calculate, one instant answer: estimated due date, how many weeks pregnant you are right now, your trimester and a timeline of the milestones ahead. Nothing you type is sent or stored.
From your last menstrual period (LMP)
The usual method: the due date falls 280 days after the first day of your last period (Naegele’s rule). Adjust your cycle length if it differs from 28 days.
Between 20 and 45 days. Defaults to 28.
Enter a date to run the calculation.
Important information
- This estimate is indicative only. It is not medical advice and is no substitute for a consultation: only a healthcare professional (midwife, obstetrician, doctor) can confirm your due date, normally from a dating scan.
- The calculation assumes a standard 28-day cycle with ovulation on day 14. Only around 4% of births happen on the exact estimated due date; a birth counts as full term between 37 and 41 weeks.
- None of the dates you enter are sent to our servers, stored, or added to the page address. Everything is calculated in your browser. Sharing is optional: if you turn it on, only the tool link and the estimated due date are shared — never the dates you typed.
Method: Naegele’s rule (due date = LMP + 280 days); conception dating (+266 days); scan-based extrapolation. Terminology: "weeks pregnant" is counted from the last menstrual period, which is two weeks more than the time since conception.
How a due date is calculated
In obstetrics a pregnancy lasts on average 280 days — 40 weeks — counted from the first day of the last menstrual period. That is Naegele’s rule, formulated in the nineteenth century and still in everyday use. It assumes a regular 28-day cycle with ovulation on day 14, which is why the cycle-length field above shifts the result by however many days your own cycle differs from the norm.
Two ways of counting coexist and are easily confused. "Weeks pregnant" is measured from the last period, and that is the figure clinicians use. Time since conception is roughly two weeks less: someone who is 12 weeks pregnant conceived about 10 weeks ago. The calculator shows both figures side by side so nothing gets lost in translation at an appointment.
Using the calculator
- Pick your method: last period, conception date, or a dating scan if you have already had one.
- Enter the matching date. For the LMP method, adjust your cycle length if it is not 28 days.
- Read your estimated due date, the week you are in and the milestone timeline — then create a countdown to the birth if you would like one.
Frequently asked questions
Count the days since the first day of your last period and divide by seven. The whole number gives the weeks, the remainder the days: 87 days means 12 weeks and 3 days pregnant. The calculator does this for you and shows the time since conception alongside, which is always two weeks less.
Because they count from a different starting point. Clinical practice counts from the last menstrual period; some tools count from conception, roughly fourteen days later. The gap is constant, so a "10 weeks since conception" reading and a "12 weeks pregnant" reading describe the same pregnancy.
It is a statistical estimate, not a prediction. Fewer than 4% of births happen on the exact calculated date, and a birth is considered full term anywhere between 37 and 41 weeks. A first-trimester dating scan remains the medical reference: if your scan gives a different date, the scan takes precedence.
No. The calculation runs entirely in your browser: no date is sent to a server, saved, or written into the page address. Sharing is only offered after you explicitly ask for it, and it passes on the due date alone, never the dates you entered.
