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When Did I Get Pregnant Calculator
What you know
Example: last period August 1, 2026 — likely conception August 10–20, 2026 (most likely August 15); due date May 8, 2027.
Behind the numbers
How your conception range is estimated
Pregnancy is dated from the first day of the last period, and conception usually happens around ovulation — about 14 days after the period starts in a typical 28-day cycle. But ovulation does not happen on the same day for everyone, and sperm can live inside the body for up to 5 days, so conception could have happened a few days before or after ovulation. That is why this calculator gives a range of about 10 days (ovulation day, plus or minus 5 days) instead of pretending to know one exact day. If you enter a due date instead, the calculator works backwards: the last period was about 280 days before the due date, and conception was about 266 days before it. If you already know the conception date, it simply adds 266 days to get the due date and shows a small range around the date you entered.
For a last period starting August 1, 2026: likely ovulation = August 1 + 14 days = August 15, 2026. The likely conception range is ovulation ± 5 days = August 10 to August 20, 2026. The due date = last period + 280 days = August 1, 2026 + 280 days = May 8, 2027. Working backwards from that due date gives the same answer: May 8, 2027 − 266 days = August 15, 2026, with the same August 10–20 range.
Examples
Example conception ranges
| What you know | Likely conception range | Due date |
|---|---|---|
| Last period August 1, 2026 | August 10–20, 2026 | May 8, 2027 |
| Last period January 15, 2026 | January 24 – February 3, 2026 | October 22, 2026 |
| Due date May 8, 2027 | August 10–20, 2026 | May 8, 2027 |
| Conception August 15, 2026 | August 10–20, 2026 | May 8, 2027 |
Tips
No online calculator can name the exact day — sperm can survive up to 5 days, so conception may have happened days before ovulation.
If your cycles are irregular or much longer or shorter than 28 days, the ovulation estimate (period + 14 days) can be off by a week or more — an early ultrasound is far more accurate.
If you tracked ovulation with tests or temperature, use that date instead: it narrows the range a lot.
Only a dating ultrasound in the first trimester can pin the timing down to within a few days — ask your doctor about it.
Good to know
Frequently asked questions
Why a range and not an exact day?
Because conception is not a single known moment. Ovulation day varies, and sperm can live up to 5 days waiting for the egg. A 10-day range around the most likely day is the honest answer.
Can I work it out exactly from my due date?
Not exactly. The due date itself is an estimate (last period + 280 days), so working backwards gives the same kind of range — usually within a few days of the true date, but not exact.
What if my cycles are not 28 days?
Then ovulation is probably not on day 14. A rough rule is that ovulation happens about 14 days before the next period, not 14 days after the last one — so a 35-day cycle means ovulation around day 21. The calculator assumes a typical cycle, so treat its range as wider if your cycles vary.
Is this medical advice?
No. This is a general estimate for planning and curiosity. For dating a pregnancy, paternity questions, or any medical decision, talk to your doctor — only an ultrasound and clinical history can give a reliable answer.