Pregnancy Weeks Calculator
Quick answer
Find out exactly how many weeks and days of pregnancy you are in, your current trimester, your estimated due date and how many days remain — calculated from your last period or, if you prefer, backwards from a known due date.
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Your details
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How it is calculated
Due date = first day of last period + 280 days (Naegele’s rule)
Current day of pregnancy = today − first day of last period
Current week = floor(days ÷ 7) · day of week = days mod 7
Trimesters: weeks 1–13 · 14–27 · 28–40+
Days remaining = due date − today · progress = current day ÷ 280
If you enter a due date instead, the last period is assumed to be 280 days earlier. Dating starts from the last period, so conception happens around “week 2” — the first two weeks of pregnancy precede conception.
Worked example
- 1
Your last period started March 1 and today is September 22.
- 2
You are 205 days into the pregnancy → week 29, with 205 mod 7 = 2 days, so “29 weeks, 2 days”.
- 3
Due date = March 1 + 280 days ≈ December 6, leaving about 75 days.
- 4
Progress ≈ 205 ÷ 280 = 73% complete.
What happens this trimester
| Your result | Category | What it means |
|---|---|---|
| Weeks 1–13 | First trimester | Major organs are forming and hormones surge. Fatigue, nausea and breast tenderness are common, and many people find symptoms ease as the second trimester begins. |
| Weeks 14–27 | Second trimester | Often the most comfortable stage — growth accelerates, the baby’s movements become noticeable, and energy frequently improves. |
| Weeks 28–40+ | Third trimester | The baby gains weight fastest and space gets tight — shortness of breath, backache and frequent urination are common as the due date approaches. |
Generic, non-diagnostic descriptions — every pregnancy is different, and your provider is the best guide for what to expect.
Frequently asked questions
Sources & further reading
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Estimate your pregnancy due date (Naegele’s rule).
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Open calculatorThis calculator provides general estimates for informational purposes only and is not medical advice. For personal guidance, consult a qualified healthcare provider.