🩺 Due Date Calculator: Estimated Due Date and Weeks Pregnant

Estimate your pregnancy due date and weeks pregnant with our precise calculator. Enter LMP, conception, or IVF date for an accurate estimate.

Last updated: 18 October 2026

Due Date Calculator: Estimated Due Date and Weeks Pregnant

Short answer

This due date calculator estimates a due date and gestational age from a date you enter. It uses exact day counts, not month arithmetic, and the result is an estimate for discussion with a clinician.

Use this pregnancy calculator if you know the first day of your last menstrual period (LMP), a known conception date, or an IVF transfer date. It shows the estimated due date, how many weeks pregnant you are today, and days remaining.

It does not predict a birth date, confirm pregnancy dating, or replace prenatal care.

Calculator

How to use this due date calculator

Choose LMP, conception date, or IVF transfer date.
Enter the date. For IVF, choose day 3 or day 5.
Review the estimated due date, gestational age, and days remaining.
Take the estimate to your first prenatal visit for clinician confirmation.

How the due date is calculated

This calculator uses exact day counts on a real calendar, including leap years. It does not use month arithmetic.

LMP method: estimated due date = LMP date + 280 days.
Conception method: estimated due date = conception date + 266 days.
IVF method: estimated due date = transfer date + 261 days for a day 5 embryo, or + 263 days for a day 3 embryo.

Gestational age is counted from an estimated pregnancy start that is 280 days before the estimated due date. It is shown as whole weeks plus whole days.

Calculating due date with month subtraction can differ by a few days from exact day counting. This tool uses exact days.

Worked examples

Exact-day examples used to check the arithmetic
Input	Method	Estimated due date
2026-01-01	LMP + 280 days	2026-10-08
2026-01-15	Conception + 266 days	2026-10-08
2026-02-01, day 5 embryo	IVF transfer + 261 days	2026-10-20
2026-02-01, day 3 embryo	IVF transfer + 263 days	2026-10-22
2024-02-29	LMP + 280 days	2024-12-05

For LMP 2026-01-01, gestational age is 12 weeks 6 days on 2026-04-01 and 40 weeks 0 days on 2026-10-08.

Comparison tables

Methods supported by this calculator
Method	Days added	Best used when
LMP	280	You know the first day of your last menstrual period.
Conception date	266	You know the conception date and it is not an estimate.
IVF transfer	261 or 263	You had IVF and know the transfer and embryo age.

What this calculator does not do
Topic	Status
Ultrasound redating	Not included; a clinician applies dating rules.
Fertility or ovulation prediction	Not included.
Medical advice	Not provided.

Infographic: how the dates relate

Days from estimated pregnancy start to due date

Conception is often estimated at 14 days after LMP

14 days

Full pregnancy length used here

280 days

IVF day 5 transfer to due date

261 days

Included

Due date from LMP, conception, or IVF transfer
Gestational age in weeks and days
Days remaining or past due date

Not included

Ultrasound redating rules
Fertility or ovulation prediction
Medical advice or diagnosis

Common mistakes and key conditions

Using month arithmetic instead of exact days can change the date by a few days.
Entering the positive pregnancy test date instead of the LMP.
Assuming the estimated due date is the day the baby will be born.
Using an unverified conception date.
Ignoring clinician dating, especially after ultrasound.

Frequently asked questions

How does a due date calculator work?

A due date calculator adds a fixed number of days to a starting date. This one uses 280 days after LMP, 266 days after conception, or 261 or 263 days after an IVF transfer.

Is the due date exact?

No. A due date is an estimate. Few babies are born on the exact estimated due date.

Can I calculate due date from conception?

Yes, if the conception date is known. This calculator adds 266 days. It is not a conception calculator, ovulation predictor, or fertility tool.

How many weeks pregnant am I?

The result shows gestational age in whole weeks and days as of today, based on the date and method you entered.

Why can different pregnancy due date calculators disagree?

Different tools may use month arithmetic, different day counts, or different dating rules. This tool uses exact day counts and states its assumptions.

Does this pregnancy calculator replace medical care?

No. Only a clinician can confirm dating, especially with ultrasound or a non-regular cycle.

Glossary

LMP: The first day of the last menstrual period.
Gestational age: Time since the estimated start of pregnancy, in weeks and days.
Estimated due date: The date 280 days after the estimated pregnancy start.
IVF transfer: Placement of an embryo into the uterus during in vitro fertilization.

Official references and last checked

Starting points for verification: ACOG Committee Opinion No. 700, Methods for Estimating the Due Date; CDC and NIH pages on gestational age.

Last updated: 2026-10-18.

Limitations, exclusions, and assumptions

Estimates assume a regular cycle and a 280-day pregnancy length.
Ultrasound redating, irregular cycles, multiple pregnancy, and clinical exceptions are not handled.
No cycle-length adjustment is applied.
The tool is not medical advice and does not predict a birth date.
Day 6 IVF values are not included.

Privacy

Calculations run in your browser. This calculator does not save, share, email, or print pregnancy data.

Due Date Calculator: Estimated Due Date and Weeks Pregnant

🩺 Due Date Calculator: Estimated Due Date and Weeks Pregnant