Pregnancy Due Date Calculator

What is the Pregnancy Due Date Calculator?

Estimate a pregnancy due date from the first day of the last menstrual period (Naegele’s rule). Naegele’s rule estimates a due date as 280 days after the first day of the last period, adjusted here for cycles longer or shorter than 28 days.

How to use the Pregnancy Due Date Calculator

1. Enter your first day of last period, your average cycle length.
2. Results update automatically as you type; you can also press Calculate.
3. Read the output: estimated due date, conception (approx.), end of first trimester.
4. Use the 📊 chart to see the result visually, then copy or share it.

Formula and method

Worked example

With first day of last period = 2026-03-01, average cycle length = 28 days, the Pregnancy Due Date Calculator returns estimated due date: Sunday, December 6, 2026; conception (approx.): Sunday, March 15, 2026; end of first trimester: Saturday, June 6, 2026.

Where the Pregnancy Due Date Calculator helps in real life

You have just had a positive test and want a rough due date before your first appointment. The estimate helps you think about timing at work and when to share the news.

Your cycles are usually 32 days long rather than 28. Entering your cycle length shifts the estimate to better reflect when ovulation probably happened.

Common mistakes to avoid

• Treating the due date as the day the baby will arrive.
• Entering the date of conception instead of the first day of the last period.
• Ignoring a different date given by an early ultrasound.
• Forgetting to adjust for longer or shorter cycles.

💡 Practical tip: Only a small share of babies are born on their exact due date — most arrive within about two weeks either side.

Tips for better results

• Confirm the estimate with your midwife or doctor.
• Use the date to plan appointments and leave, not a precise delivery day.
• Note that early ultrasound dating usually takes priority over this estimate.

⚠️ This tool provides general information and is not medical advice. It is not a substitute for diagnosis or treatment by a qualified healthcare professional.

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