Pregnancy Due Date Calculator

Estimate your baby’s due date using the first day of your last menstrual period and your menstrual cycle length.

Calculate your estimated due date

Enter the first day of your last period and adjust the cycle length if your cycle is shorter or longer than 28 days.

First day of your last menstrual period

Average cycle length

Please enter a valid last menstrual period date.

Your estimated due date

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Last menstrual period	—
Cycle length	—
Cycle adjustment	—
Estimated due date	—

Step-by-step calculation

Step 1: Start with your last menstrual period

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Step 2: Calculate the standard due date

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Step 3: Adjust for cycle length

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Step 4: Estimated due date

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What does the result mean?

The estimated due date is an approximate date when your pregnancy reaches about 40 weeks from the first day of your last menstrual period.

A due date is an estimate rather than an exact prediction. Pregnancy commonly lasts between 37 and 42 weeks from the first day of the last menstrual period. :contentReference[oaicite:1]{index=1}

Your healthcare professional may use information from an early pregnancy or dating ultrasound to establish or adjust the estimated due date. :contentReference[oaicite:2]{index=2}

How is the due date calculated?

The standard calculation uses 280 days, or 40 weeks, from the first day of the last menstrual period.

The standard estimate assumes a 28-day menstrual cycle. If your average cycle is longer or shorter, this calculator adjusts the estimate by the difference from 28 days.

Due date example

Suppose the first day of the last menstrual period was January 1, 2026 and the average cycle length was 28 days.

Standard pregnancy length = 280 days

January 1, 2026 + 280 days

Estimated due date = October 8, 2026

This gives an estimated due date of October 8, 2026.

Formula used

Standard due date = LMP + 280 days

Cycle adjustment = average cycle length − 28 days

Adjusted due date = LMP + 280 days + cycle adjustment

LMP means the first day of the last menstrual period. The cycle-length adjustment is used when the average menstrual cycle differs from 28 days.

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Important: This calculator provides an estimated due date for general informational purposes. It cannot determine the exact date of conception or delivery. Due dates may be revised by your healthcare professional based on clinical assessment or ultrasound dating. If you are pregnant, discuss your estimated due date and pregnancy care with your doctor, midwife, or other qualified healthcare professional. :contentReference[oaicite:3]{index=3}