Health calculator
Pregnancy Due Date Calculator
Estimate your due date and how many weeks pregnant you are.
Quick answer
How is a pregnancy due date calculated?
Add 280 days (40 weeks) to the first day of your last menstrual period. If your period started January 1, 2026, your due date is October 8, 2026. From a known conception date, add 266 days instead.
Naegele's rule: due date = first day of last period + 280 days (40 weeks), plus (cycle length − 28) days. From conception: + 266 days. IVF: 3-day transfer + 263 days, 5-day transfer + 261 days.
⚡ Answer updates as you type · Enter = calculate · Esc = reset
- Due date = first day of last period + 280 days = November 25, 2026.
- Pregnancy is counted from February 18, 2026 (2 weeks before conception).
- End of 1st trimester (13w6d): May 26, 2026
- End of 2nd trimester (27w6d): September 1, 2026
- Full term begins (39 weeks): November 18, 2026
- Only about 4% of babies arrive on the due date — most come within 2 weeks of it. Always confirm with your doctor or midwife.
Estimate your baby's due date from your last period, conception date, or IVF transfer — with how many weeks pregnant you are and key trimester dates.
About this Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator estimates your baby's due date from the first day of your last period (adjusted for your cycle length), your conception date, or an IVF embryo transfer date. It also shows how many weeks and days pregnant you are today, your trimester, and key milestone dates. This is an estimate — always confirm with your doctor or midwife.
What you'll need
- • Method: last period, conception, or IVF transfer
- • Date
- • Average cycle length (last period method)
How it works
- 1. Choose how you want to calculate.
- 2. Pick the date.
- 3. Adjust cycle length if it isn't 28 days.
- 4. Read your due date and weeks pregnant.
- 5. See trimester and full-term dates.
Worked example
Last period began March 10 with a 30-day cycle: March 10 + 280 days + 2 days = December 17. On June 2 you would be 12 weeks 0 days pregnant, in the first trimester.
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Pregnancy Due Date Calculator FAQ
What is the Pregnancy Due Date Calculator?
The Pregnancy Due Date Calculator is a free online tool that helps you estimate your due date and how many weeks pregnant you are.
How do I use the Pregnancy Due Date Calculator?
Open the Pregnancy Due Date Calculator, enter the requested values, and review the instant estimate on the page.
Is the Pregnancy Due Date Calculator free?
Yes. The Pregnancy Due Date Calculator is free to use on Fast Online Calculator and does not require an account.
How accurate is a due date?
It's an estimate. Only about 4% of babies are born on their due date; most arrive within two weeks before or after it. An early ultrasound can refine it.
How many weeks pregnant am I?
Count from the first day of your last period. The calculator shows weeks and days pregnant for today automatically.
When does each trimester start?
First trimester: weeks 1–13. Second: weeks 14–27. Third: week 28 until birth.
Why is pregnancy counted from the last period?
Most people know that date but not the exact conception date, so doctors count from it — about 2 weeks before conception.
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