Due Date Calculator
Estimated due date and current week from your last period.
days
Enter the first day of your last menstrual period.
Formula
due date ≈ last period + 280 daysHow it works
Estimates a due date using Naegele's rule (280 days from the last period), adjusted for cycle length.
Example
A 28-day cycle puts the due date 40 weeks after the first day of the last period.
For general information only, not medical advice. Individual needs vary — consult a qualified health professional. Only an ultrasound dating scan gives an accurate due date.
About the Due Date Calculator
Estimated due date and current week from your last period. It sits in the Health & Fitness section of NWS Calc, a free collection of calculators that run entirely in your browser. There is no signup, no paywall and no tracking — open the page, enter your numbers, get an answer.
Frequently asked questions
- Is the Due Date Calculator free to use?
- Yes. Every calculator on NWS Calc is completely free, with no signup, no usage limits and no ads.
- Does my data leave my device?
- No. The Due Date Calculator runs entirely in your browser using JavaScript. Nothing you type is uploaded, logged or stored on a server.
- Can I use the Due Date Calculator on my phone?
- Yes. The page is fully responsive and works in any modern mobile or desktop browser — there is nothing to install.
- What else is in Health & Fitness?
- BMI, body fat, calories, macros, heart rate and training numbers. You can browse the full Health & Fitness category for related calculators.