Pregnancy Due Date Calculator

Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP.

Pregnancy Due Date Calculator

Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP.

Last menstrual period (LMP)

Enter values above and click Calculate — results will appear here with the formula explained.

Due date = LMP + 280 days (40 weeks) = LMP + 1 year - 3 months + 7 days

How does this work?

Naegele's rule estimates due date as 280 days from the first day of last menstrual period, assuming a 28-day cycle and ovulation on day 14. It yields 40 weeks gestation.

This is an estimate for informational purposes only, not medical advice. Ultrasound dating is more accurate — confirm with a clinician, especially with irregular cycles.

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Disclaimer: Results are estimates for informational purposes only and do not constitute professional medical advice.

Quick Answer

Pregnancy Due Date Calculator: Estimate due date from last menstrual period (LMP) using Naegele's rule — 280 days or 40 weeks from LMP. Formula: Due date = LMP + 280 days (40 weeks) = LMP + 1 year - 3 months +.

How to Use This Calculator

1Enter the first day of your last menstrual period.
2Calculate to see estimated due date and weeks.
3Use with cycle length variations: longer cycles may shift ovulation later, adjust with clinician guidance.

Formula Used

Due date = LMP + 280 days (40 weeks) = LMP + 1 year - 3 months + 7 days

Naegele's rule estimates due date as 280 days from the first day of last menstrual period, assuming a 28-day cycle and ovulation on day 14. It yields 40 weeks gestation.

This is an estimate for informational purposes only, not medical advice. Ultrasound dating is more accurate — confirm with a clinician, especially with irregular cycles.

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Worked Example

If LMP is 2026-01-01, adding 280 days gives due date 2026-10-08, about 40 weeks later.

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Frequently Asked Questions

QWhat if my cycle is not 28 days?

Naegele's assumes 28 days. With 35-day cycles, ovulation is later, so due date may be about a week later — discuss with your provider.

QDoes IVF change due date?

IVF uses transfer or retrieval date, not LMP, for more precise dating — this tool is for natural conception LMP.

QIs this medical advice?

No, it is educational. Always confirm with a healthcare professional.

Formula Used

Due date = LMP + 280 days (40 weeks) = LMP + 1 year - 3 months + 7 days

Naegele's rule estimates due date as 280 days from the first day of last menstrual period, assuming a 28-day cycle and ovulation on day 14. It yields 40 weeks gestation.

This is an estimate for informational purposes only, not medical advice. Ultrasound dating is more accurate — confirm with a clinician, especially with irregular cycles.

Frequently Asked Questions

QWhat if my cycle is not 28 days?

Naegele's assumes 28 days. With 35-day cycles, ovulation is later, so due date may be about a week later — discuss with your provider.

QDoes IVF change due date?

IVF uses transfer or retrieval date, not LMP, for more precise dating — this tool is for natural conception LMP.

QIs this medical advice?

No, it is educational. Always confirm with a healthcare professional.