Pregnancy Due Date Calculator
Estimate a due date from the first day of the last menstrual period and cycle length.
← Browse all calculatorsPregnancy Due Date Calculator
Estimate a due date from the first day of the last menstrual period and cycle length.
An estimate only. NHS guidance says a 12-week scan can estimate gestation more accurately.
How to use this calculator
Enter your values above and the result updates instantly. You can change the inputs as often as you like, and use Reset to restore the example values.
About the result
Estimate a due date from the first day of the last menstrual period and cycle length. The calculation runs in your browser; the values you enter are not sent to this website.
What the Pregnancy Due Date Calculator does
Estimate a due date from the first day of the last menstrual period and cycle length. It is designed for understanding a general health or activity estimate from the measurements you provide. The calculator uses the values you enter to produce estimated due date and estimated conception date without sending your information to the server.
This page is most useful when you want a quick answer and a repeatable way to compare alternatives. Change one input at a time to see which factor has the greatest effect.
How the calculation works
The calculation starts with first day of last period and usual cycle length. It applies the relevant health relationship to calculate estimated due date and estimated conception date. Results update in your browser whenever an input changes.
Inputs used
- First day of last period
- Usual cycle length
Results provided
- Estimated due date
- Estimated conception date
Practical tip: Use recent, accurately measured inputs and treat the output as one indicator rather than a diagnosis.
Example pregnancy due date calculator setup
The calculator opens with the example values below. They demonstrate the expected format and give you a starting point before entering your own figures.
- First day of last period
- 2026-05-01
- Usual cycle length
- 28 days
After entering the values, review estimated due date and estimated conception date in the results panel. Use Reset whenever you want to return to this example.
Understanding your result
Read the result alongside the inputs that produced it. A precise-looking number is still only as useful as the information entered. For comparisons, keep every input the same except the one factor you want to test.
This tool is for general information only and is not a substitute for medical advice, diagnosis or treatment. The tool rounds displayed answers where appropriate, while the underlying browser calculation retains greater precision.
Frequently asked questions
What information do I need for the Pregnancy Due Date Calculator?
You need first day of last period and usual cycle length. Use values that describe the same scenario and measurement period so the comparison remains meaningful.
What does the Pregnancy Due Date Calculator show?
The results cover estimated due date and estimated conception date. Change any input to compare another scenario; the answer updates immediately.
Can I rely on this health calculation?
This tool is for general information only and is not a substitute for medical advice, diagnosis or treatment.
Sources and further guidance
Time-sensitive assumptions on this page were checked against the following primary guidance: