Pregnancy Due Date Calculator

What Is a Pregnancy Due Date Calculator?

The moment a pregnancy is confirmed, the first question is almost always the same: when is the baby due? A due date calculator answers it in seconds. The standard medical estimate is 40 weeks (280 days) from the first day of your last menstrual period — a rule known as Naegele's rule that doctors and midwives have used for over 200 years.

This tool is for anyone who has just seen those two lines: expectant parents planning the months ahead, partners booking time off, or grandparents doing the maths. Beyond the headline date, it shows how far along you are right now, which trimester you are in, and the estimated conception date — the key facts your midwife will ask for at the first appointment. It also handles known conception dates and IVF transfers, where the counting works a little differently.

How to Use This Due Date Calculator

1. Choose your method. Most people should pick "First day of last menstrual period (LMP)". If you know the exact conception date (for example from ovulation tracking), choose that instead; for IVF, choose the embryo transfer date.
2. Enter the date. Use the calendar picker — the first day of your last period, the conception date, or the transfer date, depending on your method.
3. Click "Calculate Due Date". You will see your estimated due date, your current weeks and days pregnant, your trimester, and how many days remain.

Worked Example: Last Period 5 January 2026

Let us apply Naegele's rule step by step. Suppose the first day of the last period was 5 January 2026:

1. Add 280 days: a full-term pregnancy averages 40 weeks = 280 days
2. Count forward: 5 January + 280 days lands on Monday, 12 October 2026
3. Estimated conception: roughly 14 days after the last period began — about 19 January 2026

For a known conception date the tool instead adds 266 days (38 weeks), and for an IVF transfer it adds 266 days for a day-5 blastocyst transfer. Try your own date in the calculator above — then write the result down, because everyone from your midwife to your employer will ask for it.

Tips for Using Your Due Date

• Book your first antenatal appointment early. In many countries the first scan happens around 8–12 weeks — count forward from your last period, not from the due date backwards.
• Know your trimester. Trimester 1 runs to 13 weeks 6 days, trimester 2 to 27 weeks 6 days, and trimester 3 to birth — each brings different milestones and screening tests.
• Plan around the window, not the day. Schedule leave and childcare to cover two weeks before and after the due date.
• Track weekly, not daily. Pregnancy is measured in weeks and days (e.g. 24+3) — that is the language every midwife speaks.
• Eat and rest for two — sensibly. You need only about 340 extra calories a day in the second trimester and 450 in the third; sleep and folate matter more than eating double.
• When in doubt, call your provider. No calculator replaces professional care — report reduced movement, bleeding or severe headaches promptly.

Frequently Asked Questions