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
Conception Date Calculator
Works backward from how many days remain until a known due date to estimate when conception occurred (and how far along you are). Switch the basis to LMP to account for your cycle length and luteal phase.
Fill in the required fields to see your result.
Key differences
| Conception Date Calculator | Conception Date Calculator | |
|---|---|---|
| Category | Pregnancy | Pregnancy |
| Inputs required | 1 | 4 |
| Result | Days since conception (days ago) | Estimated Conception |
| 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. | Works backward from how many days remain until a known due date to estimate when conception occurred (and how far along you are). Switch the basis to LMP to account for your cycle length and luteal phase. |