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Pregnancy Due Date Calculator

Estimate your pregnancy week and days remaining until your due date using Naegele's rule (LMP + 280 days). Adjusted for your menstrual cycle length.

Days Since Last Menstrual Period (LMP)

days

Menstrual Cycle Length

days

Fill in the fields above and click Calculate to see your results.

How to use

Estimate your pregnancy week and days remaining until your due date using Naegele's rule (LMP + 280 days). Adjusted for your menstrual cycle length.

How it's calculated

Cycle Adjustment (days)

cycle_length - 28

Days added or subtracted for cycles longer or shorter than 28 days

Days Pregnant

lmp_days_ago + adjusted_lmp_offset

Estimated number of days since conception (adjusted for cycle length)

Weeks Pregnant

floor(days_pregnant / 7)

Current week of pregnancy (Naegele's rule: LMP + 280 days = due date)

Days Until Due Date

max(0, 280 - days_pregnant)

Days remaining until estimated due date (40 weeks = 280 days from LMP)

Weeks Until Due Date

floor(days_remaining / 7)

Full weeks remaining until estimated due date

Examples

LMP 14 days ago, standard 28-day cycle

Menstrual Cycle Length:28
Days Since Last Menstrual Period (LMP):14

LMP 70 days ago, standard 28-day cycle

Menstrual Cycle Length:28
Days Since Last Menstrual Period (LMP):70

Frequently Asked Questions

What is Naegele's rule?

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). It assumes a standard 28-day cycle. This calculator adjusts for longer or shorter cycles by shifting the estimate accordingly.

Why does cycle length affect the due date?

Naegele's rule assumes ovulation occurs on day 14 of a 28-day cycle. If your cycle is 35 days, ovulation likely occurs around day 21, meaning conception happened later — so the due date shifts forward by 7 days. The calculator adds (cycle_length - 28) days to account for this.

How accurate is this calculator?

This calculator provides an estimate based on Naegele's rule, which is the standard clinical method. However, actual due dates can vary by 2 weeks in either direction. An ultrasound scan in the first trimester provides a more accurate estimate. Always confirm your due date with a qualified healthcare provider.