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. Consult a qualified professional for decisions.

What is Pregnancy Due Date?

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

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 +.

What it does: 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 + 7 days
Inputs: Last menstrual period (LMP)
Example: If LMP is 2026-01-01, adding 280 days gives due date 2026-10-08, about 40 weeks later.

Calculator Inputs at a Glance

Field	What to enter
Last menstrual period (LMP)	Enter a value

All fields use the exact formulas shown below — results include step-by-step breakdowns you can verify by hand.

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.

Quick Answer

What it does: 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 + 7 days

Inputs: Last menstrual period (LMP)

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

Field

What to enter

Last menstrual period (LMP)

Enter a value

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.