Pregnancy Calculator
Enter the first day of your last period to see how many weeks and days pregnant you are today, your due date and key dates ahead.
This calculator gives general estimates for information only. It is not medical advice and does not replace a consultation with a doctor or other qualified health professional.
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The formula
Gestational age = today - first day of last period. Due date = that day + 280 days.
Weeks and days, not months
Pregnancy is counted in weeks and days. "Twenty weeks and three days" is the standard way to say how far along you are. Nine months is only a rough summary, because the 40 weeks are closer to nine and a quarter months.
What the result shows
- Weeks and days pregnant today, and which trimester that is
- Your estimated due date and the days left
- The date your first and second trimesters end
- The date you reach full term at 37 weeks
A few milestones
Most people have a first scan at around 8 to 14 weeks and an anatomy scan at around 18 to 22 weeks. Your care team will confirm the schedule that applies to you.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| First day of last period; First day of last period: 2026-01-10; Average cycle length (days): 28 | Estimated due date: Saturday, October 17, 2026 |
| First day of last period; First day of last period: 2026-03-22; Average cycle length (days): 28 | Estimated due date: Sunday, December 27, 2026 |
| First day of last period; First day of last period: 2026-05-05; Average cycle length (days): 32 | Estimated due date: Friday, February 5, 2027 |
Pregnancy Calculator: frequently asked questions
How accurate is an estimated due date?
Only about 4 in 100 babies arrive on the due date. Most are born within two weeks either side. Treat the date as the middle of a window, and follow your midwife or doctor, who may adjust it after a scan.
Why do doctors count from the last period if conception happens two weeks later?
Because most people remember the start of their last period but not the exact day of conception. Pregnancy weeks are counted from that date, so you are already "two weeks pregnant" at conception.
Can I rely on this result as medical advice?
No. It is a general estimate for information only. It cannot replace a check-up, and your doctor can interpret the numbers for your own situation.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026