Toolkit Shelf

Health Calculators

Due Date Calculator

Use this due date calculator to estimate a pregnancy due date from the first day of the last menstrual period and average cycle length.

Reviewed May 25, 2026EstimateFormula shown

Live calculator

Due date calculator

Estimated due dateFeb 5, 2027

Based on last menstrual period plus 280 days, adjusted for cycle length.

Estimated conceptionMay 15, 2026

Approximate ovulation timing for planning context.

Weeks pregnant3.6 weeks

First trimester estimate ends around Aug 6, 2026.

Formula

Due date estimate

Due date = first day of last period + 280 days + cycle adjustment

This is a common estimate and does not replace ultrasound dating or medical care.

How to use

Steps

  1. Enter the first day of the last menstrual period.
  2. Enter average cycle length.
  3. Review estimated due date and conception timing.
  4. Confirm important pregnancy dates with a qualified clinician.

Example

Sample calculation

Last periodMay 1, 2026
Cycle length28 days
Estimated due dateFeb 5, 2027

Calculator use

Best for

  • Quick estimated due date from first day of last period and average cycle length.
  • Wellness, nutrition, pregnancy, or fitness planning when a rough estimate is enough.
  • Scenario comparisons before changing calorie, macro, or body-measurement assumptions.
  • Planning alongside professional medical or nutrition advice, not as a diagnosis.

Before relying on it

Check first

  • Entering first day of last period and average cycle length from different time periods or scenarios.
  • Treating a calculator result as medical advice or a diagnosis.
  • Using stale body, activity, pregnancy, or nutrition inputs when your situation has changed.
  • Ignoring context such as age, medication, training status, medical history, or professional guidance.

Benchmarks

How to read the result

The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions.

280 daysStandard estimate

A common due date estimate from last menstrual period.

Cycle adjustmentPersonalized

Longer or shorter cycles can shift the estimate.

UltrasoundClinical dating

Medical dating can differ from calculator estimates.

Calculator accuracy

Methodology and assumptions

The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.

Formula

Due date = first day of last period + 280 days + cycle adjustment

Inputs used

First day of last period, Average cycle length

Limitations

Results are estimates for quick planning and should be checked before important financial, legal, tax, health, or business decisions.

Last reviewed

May 25, 2026

Cite this page

Toolkit Shelf. Due Date Calculator. Retrieved May 25, 2026, from https://toolkitshelf.com/tools/due-date-calculator

FAQ

Common questions

How is a pregnancy due date estimated?

A common estimate adds 280 days to the first day of the last menstrual period, adjusted for cycle length.

Is this due date exact?

No. It is an estimate. A clinician may use ultrasound and medical history for dating.

Why does cycle length matter?

Cycle length can shift estimated ovulation timing, which can shift the due date estimate.