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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.

Method and assumptions documentedPlanning estimateSource note includedNo expert review claimed

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 pregnant16 weeks

First trimester estimate ends around Aug 6, 2026.

Use this as a planning estimate, not medical advice. Medical conditions, medication, pregnancy, eating disorder history, or disease-specific nutrition needs should be handled with a qualified professional.

Quick answer

Due Date Calculator: what it calculates

Due Date Calculator calculates estimated due date from first day of last period and average cycle length. The visible formula is Due date = first day of last period + 280 days + cycle adjustment.

ResultEstimated due date
InputsFirst day of last period, Average cycle length
FormulaDue date estimate

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

  • Use this due date calculator to estimate a pregnancy due date from the first day of the last menstrual period and average cycle length.
  • Estimating due date, pregnancy week, trimester, or conception timing for planning conversations.
  • Checking date assumptions from last menstrual period, due date, or cycle length with the method visible.
  • Preparing non-diagnostic timing context before confirming dates with a qualified clinician.

Before relying on it

Check first

  • Treating pregnancy date estimates as diagnosis, medical advice, or a substitute for clinician dating.
  • Ignoring cycle variability, ultrasound timing, fertility treatment dates, irregular periods, or clinician guidance.
  • Using late or uncertain dates as if they were exact conception or due-date proof.

Details

What to know before using the result

Dating methodLMP plus 280 days

The estimate starts from the first day of the last menstrual period and adds about 40 weeks.

Cycle lengthRough adjustment

Longer or shorter average cycles can shift estimated ovulation timing, but irregular cycles can make dating less reliable.

Clinical datingConfirm with clinician

A clinician may update the estimated due date based on ultrasound, assisted reproduction dates, or other clinical information.

Source notes

References used for this calculator

ACOGStates that estimated due date is calculated from the first day of the last menstrual period and average pregnancy length is 280 days or 40 weeks.ACOGProvides clinical guidance on methods for estimating due date and recording gestational age.

Benchmarks

How to read the result

280 days: Standard estimate.

A common due date estimate from last menstrual period.

Cycle adjustment: Personalized.

Longer or shorter cycles can shift the estimate.

Ultrasound: Clinical dating.

Medical dating can differ from calculator estimates.

Calculator accuracy

Methodology and assumptions

Formula

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

Inputs used

First day of last period, Average cycle length

Limitations

Health results are screening or planning estimates. Age, body composition, medication, medical history, pregnancy, and professional guidance can change the right interpretation.

Review record

Method and sources checked on July 12, 2026. The documented method, source timing, validity conditions, and reliance limits were checked on this date.

Method provenanceEstimate · toolkitshelf.pregnancy-due-date-LMP.v1
Maintained by
Toolkit Shelf
Calculation class
Estimate
Method version
toolkitshelf.pregnancy-due-date-LMP.v1
Source date
May 2017; reaffirmed 2025
Source checked
July 12, 2026
Intended audience
People making a rough pregnancy due-date estimate from a known last menstrual period and average cycle length.
Valid when
The estimate assumes the last menstrual period is known and uses the entered cycle adjustment. Assisted reproduction, irregular cycles, and ultrasound findings require clinical dating.
Reliance boundary
This is an LMP-based planning estimate, not clinical dating, prenatal care, an ultrasound interpretation, or a replacement for a clinician-assigned due date.
Data freshness
ACOG Committee Opinion No. 700 and its reaffirmed status were checked on July 12, 2026.
Cite this page

Toolkit Shelf. Due Date Calculator. 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.

When should I ask a clinician?

Ask a clinician or qualified nutrition professional when pregnancy, medication, medical history, eating disorder risk, symptoms, or disease-specific guidance matters.

Why can health formulas be misleading?

Health formulas simplify age, sex, body composition, training status, measurement method, pregnancy, and medical context into a planning estimate.

Is this medical advice?

No. Health calculators are screening or planning tools and do not diagnose, treat, or replace professional medical or nutrition guidance.