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Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator estimates an expected delivery date from the first day of the last menstrual period or from a known conception date. It also shows the estimated current gestational age and major week-based milestones. A due date is an estimate, not a prediction of the exact delivery day. Cycle length, ovulation timing, assisted reproduction dates, and ultrasound findings can change clinical dating, so medical care should use the date confirmed by a qualified clinician.

Calculator inputs

days
Result
—
Estimated due date
Gestational age today—
Estimated trimester—
12-week date—
20-week date—

1. Choose the dating method

Select last menstrual period for standard cycle-based dating or conception when that date is known.

2. Enter the reference date

Use the first day of the last menstrual period, not the final day, when LMP is selected.

3. Adjust cycle length

For LMP dating, enter the typical cycle length so the estimate can shift from the 28-day assumption.

4. Review the estimated date

The page adds 280 days from adjusted LMP or 266 days from conception.

5. Confirm clinically

Use prenatal care and clinician-reviewed dating for medical decisions.

LMP method: estimated due date = first day of LMP + 280 days + (cycle length − 28 days)

Conception method: estimated due date = conception date + 266 days

The cycle adjustment is a simplified estimate. Clinical dating may use ultrasound or assisted-reproduction timing.

What the result means

Use the result as an estimate based on the values and assumptions entered.

Changing an input updates the result automatically.

Given: First day of the last menstrual period was January 1, 2026, with a typical 28-day cycle.

Calculation: January 1, 2026 + 280 days.

Result: Estimated due date = October 8, 2026.

Interpretation: This is an estimated 40-week date and should be confirmed during prenatal care.

Is the due date the day labor will begin?

No. It is a reference point, and normal delivery timing varies around that date.

Why does cycle length change the estimate?

A cycle longer or shorter than 28 days may shift the likely ovulation date in a simplified LMP model.

Which date should be used after IVF?

Assisted reproduction dating uses procedure-specific information; use the date provided by the fertility clinic.

Can ultrasound change the due date?

Yes. A clinician may revise dating based on ultrasound timing and clinical guidance.

What if the last menstrual period is uncertain?

Do not rely on this estimate alone; discuss dating with a prenatal care professional.