What it calculates
A due date is an estimate of when a baby will reach 40 weeks of pregnancy. Most babies arrive in the weeks around it rather than on the day.
How it works
From the last period the calculator applies Naegele’s rule, adjusted for cycle length. From conception it adds 266 days; from an IVF transfer it adds 263 (day 3) or 261 (day 5) days.
Formula
Due date = LMP + 280 days + (cycle length − 28)
- Conception + 266 days
- Day-3 transfer + 263 days; day-5 transfer + 261 days
How to use it
- Choose what you know: last period, conception or IVF transfer.
- Enter the date (and cycle length if using the last period).
- Read the due date and your current stage.
For a last period 8 weeks ago and a 28-day cycle:
Why it helps
- Supports IVF dating as well as the last period.
- Shows the current stage alongside the due date.
Limitations
- An ultrasound scan may revise the due date.
- Irregular cycles reduce accuracy.
Frequently asked questions
How many babies arrive on the due date?
Only a small minority. Most are born within a couple of weeks either side.
Do you store what I enter?
No. This calculator runs entirely in your browser. Your measurements and dates are not sent to or stored on our servers.
Sources
These calculators provide estimates only and are not a substitute for medical advice. Dates and ranges vary between individuals; follow the guidance of your doctor or midwife. Your inputs stay in your browser and are not stored by UrbanFiling.