What is a Due Date Calculator?
A Due Date Calculator estimates when your baby is due, based on the first day of your last menstrual period and your usual cycle length.
Doctors usually add 280 days (40 weeks) to the first day of the last period. Longer or shorter cycles shift the date. Only a small share of babies arrive exactly on the due date, and an ultrasound may give a more accurate date.
How to use the Due Date Calculator
- Enter first day of your last period.
- Tap Calculate to see the result.
- Tap Reset to clear the fields and try again.
Who should use it
- Expecting parents
- People planning leave and support
- Anyone tracking a pregnancy
Key terms
- Last menstrual period
- The first day of your most recent period.
- Cycle length
- Days from the start of one period to the start of the next.
Frequently asked questions
How accurate is the due date?
It is an estimate. Most babies are born within two weeks either side.
Can an ultrasound change the date?
Yes. Early scans are often used to confirm it.
What if my cycles are irregular?
The estimate may be less accurate. Ask your doctor.
Is this medical advice?
No. Consult a doctor.
Is my data stored?
No. Everything you enter stays in your browser and is cleared when you close the page.
Last updated: 1 November 2026