Conception Date Calculator: From Due Date, Last Period or Birth Date
Estimate the date of conception from a due date, the first day of the last period, or a birth date and the weeks of pregnancy at birth.
- Nothing you type is stored
- Free
- No signup
Estimated conception date
Wed, 11 Feb 2026
- Likely window from
- Fri, 6 Feb 2026
- Likely window to
- Thu, 12 Feb 2026
- Due date
- Wed, 4 Nov 2026
- Pregnancy counted from
- Wed, 28 Jan 2026
An estimate for general information, not medical advice. Dates can differ by a week or two; confirm with your doctor or ANM.
Sperm can live up to about 5 days, so the window runs from 5 days before to 1 day after.
Days around conception
| Date | Days from conception |
|---|---|
| Fri, 6 Feb 2026 | −5 |
| Sat, 7 Feb 2026 | −4 |
| Sun, 8 Feb 2026 | −3 |
| Mon, 9 Feb 2026 | −2 |
| Tue, 10 Feb 2026 | −1 |
| Wed, 11 Feb 2026 | 0 |
| Thu, 12 Feb 2026 | 1 |
How to use
- Choose due date, last period or birth date.
- Enter the date (and cycle length or weeks at birth if asked).
- See the estimated conception date and the likely window.
Good to know
Conception usually happens within a day of ovulation, about 14 days before the next period would have started. So conception ≈ last period + (cycle length − 14) days, or due date − 266 days.
Sperm can live up to about 5 days, so the intercourse that led to pregnancy most likely happened in the 5 days before to 1 day after ovulation (Wilcox et al., 1995). That is why the result is shown as a window, not one exact day.
Cycles vary, and due dates from scans have a margin of about a week, so the date is an estimate. It cannot prove when or with whom conception happened.
Questions
How accurate is a conception date calculator?
It usually points to the right week, but not to an exact day. Early ultrasound dating narrows it down further.
If my due date is 8 October, when did I conceive?
About 266 days earlier, around 15 January, most likely between 10 and 16 January.
Can I work it out from my baby's birthday?
Yes. Enter the birth date and how many weeks pregnant you were at birth (40 if born on the due date).
Can this tell paternity?
No. The dates are too uncertain. Only a DNA test can establish paternity.
Is my data saved?
No. Dates are calculated on your device and never sent anywhere.