See how far along you are. This free pregnancy calculator shows your weeks pregnant, trimester, due date and progress, calculated from your last period, due date or conception date.
Enter the relevant date and the calculator shows how many weeks and days pregnant you are today, your trimester, due date and progress.
Estimates only and not medical advice. Confirm your dates and follow your antenatal care with a qualified midwife or doctor.
How the Pregnancy Calculator Works
This tool works out how far along a pregnancy is today, using whichever date you already know — the first day of your last period, your due date, or a conception date. From that single date it derives everything else: weeks and days pregnant, trimester, progress, and days remaining.
Formula: From last period: due date = last period start + 280 days + (cycle length − 28). From due date: last period (derived) = due date − 280 days. From conception: last period (derived) = conception date − 14 days, and due date = conception date + 266 days. In every mode, gestational age (in days) = today − last period date; weeks pregnant = gestational age ÷ 7 rounded down, with the remainder as extra days. Trimester is First under 98 days (under 14 weeks), Second under 196 days (under 28 weeks), otherwise Third. Progress = gestational age ÷ 280 × 100%, capped at 100%.
- Calculate from — whether you’re entering your last period, your due date, or a conception date.
- Date entered — the last period start, due date, or conception date, depending on the mode selected.
- Average cycle length — optional, in days (default 28, valid range 20–45), used only in last-period mode to adjust the derived due date.
Example Scenarios
| Calculate from | Date entered | As-of date | Weeks pregnant | Trimester |
|---|---|---|---|---|
| Last period | Jan 1, 2026 | Mar 1, 2026 | 8w 3d | First |
| Last period | Jan 1, 2026 | Jun 1, 2026 | 21w 4d | Second |
| Due date | Oct 8, 2026 | Aug 1, 2026 | 30w 2d | Third |
| Conception | Feb 1, 2026 | May 1, 2026 | 14w 5d | Second |
| Last period | Jun 1, 2026 | Nov 1, 2026 | 21w 6d | Second |
Pregnancy Calculator FAQ
What’s the difference between calculating from my last period, due date, or conception date?
All three modes work out the same underlying last-period date, just from different starting points. From your last period it’s used directly; from a due date it subtracts 280 days; from conception it subtracts 14 days. Everything else — weeks pregnant, trimester, progress — is then worked out from that date.Why is gestational age counted from my last period instead of conception?
This is the standard obstetric convention because the last period date is usually known with more confidence than the exact conception date. It means “weeks pregnant” is roughly two weeks ahead of how long it’s actually been since conception.How is my trimester worked out?
The calculator classifies your gestational age in days: under 98 days (under 14 weeks) is the first trimester, 98 to 195 days (14 to 27 weeks) is the second, and 196 days or more (28 weeks or more) is the third.How is the pregnancy progress percentage calculated?
It divides your current gestational age in days by 280 (the standard 40-week pregnancy length) and converts that to a percentage, capped at 100% if you’ve passed your due date.Does adjusting my cycle length change how many weeks pregnant I am today?
No — in last-period mode, cycle length only shifts the estimated due date, not the gestational age calculated from your entered last-period date. Your “weeks pregnant” figure is always today minus your last period date, regardless of cycle length.How accurate is my calculated due date and current week?
These are estimates based on standard formulas and the date you provide, not a confirmed measurement. An ultrasound dating scan with your midwife or doctor gives a more accurate picture, especially if your cycles are irregular or your dates are uncertain.Related Calculators
Once you know your current week, the pregnancy week calculator for typical trimester and month milestones can show what’s generally happening at that stage. Curious about growth specifically, the fetal weight calculator and the baby development week-by-week calculator offer more detail on the baby’s side of things.