Pregnancy Calculator
Calculate due date, gestational age and pregnancy milestones
Pregnancy Calculator uses the standard 280-day (40-week) estimate from your last menstrual period to calculate your due date, then works out exactly how many weeks and days pregnant you are today and which trimester that falls into.
This tool gives general estimates for informational purposes only and isn't medical advice. Talk to a qualified healthcare provider about your individual health.
How to use Pregnancy Calculator
- 1
Enter the first day of your last menstrual period.
- 2
Your estimated due date appears instantly.
- 3
See how many weeks and days pregnant you are today.
- 4
See which trimester you're currently in.
Everything you need to know about pregnancy due date calculations
How a due date is typically estimated
The most common method estimates a due date as 40 weeks from the first day of the last menstrual period — a standard convention used as a starting estimate, not a guarantee, since only a small percentage of births happen exactly on the calculated date.
An important note
This tool provides a general estimate for informational purposes — it isn't a substitute for guidance from a doctor or midwife, who can refine timing using an ultrasound and your specific medical history.
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Frequently Asked Questions
Why 280 days specifically?
280 days (40 weeks) from the last menstrual period is the standard clinical convention for estimating a due date, even though actual ovulation and conception happen roughly two weeks into that window.
How are the trimesters defined here?
Weeks 1 through 12 are the first trimester, weeks 13 through 26 are the second, and week 27 onward is the third — the commonly used breakdown, though exact boundaries can vary slightly by source.
Is this a substitute for a doctor's estimate?
No — this is a quick estimate based on a standard formula. Your doctor's estimate, especially one based on an ultrasound, is more accurate for your specific pregnancy.
Does this tool send my date to a server?
Yes — the date is sent to our servers to compute the result and the result is returned to you; we don't store it.
Is this tool free to use?
Yes — completely free, with no signup required.