Compare calculators
Both calculators run independently β change the inputs on either side to compare results.
Pregnancy
Conception Date Calculator
Estimates the most likely conception date by counting back 266 days (38 weeks) from your due date. Useful when you know your due date but want to narrow down when fertilization likely occurred.
Fill in the required fields to see your result.
Pregnancy
Due Date Calculator
Estimates your baby's due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP) using Naegele's Rule. Use it in early pregnancy to plan prenatal appointments, milestones, and parental leave.
Fill in the required fields to see your result.
Key differences
| Conception Date Calculator | Due Date Calculator | |
|---|---|---|
| Category | Pregnancy | Pregnancy |
| Inputs required | 1 | 1 |
| Result | Days since conception (days ago) | Days until due date (days) |
| What it does | Estimates the most likely conception date by counting back 266 days (38 weeks) from your due date. Useful when you know your due date but want to narrow down when fertilization likely occurred. | Estimates your baby's due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP) using Naegele's Rule. Use it in early pregnancy to plan prenatal appointments, milestones, and parental leave. |