Unlikely but possible: sperm survive up to 5 days, and ovulation can come early in short or irregular cycles - sex late in a long period can overlap the fertile window.
Add the confuser: ovulation spotting and irregular bleeding get mistaken for periods. The honest odds: lowest of the cycle, not zero - and "lowest" is not a contraceptive strategy. If pregnancy is not the plan: contraception regardless of cycle day, and emergency contraception exists for the just-happened case - sooner is better.
What to do
Common questions
Can you get pregnant on your period?
Unlikely, but genuinely possible - and the myth that period sex is safe deserves retiring. The mechanics: sperm can survive up to 5 days in the reproductive tract, and ovulation - the event that matters - can come early in short or irregular cycles: a person with a 22-day cycle ovulates around day 8; sex on day 5 or 6 of a longer period leaves viable sperm waiting when the egg arrives. Add the confuser: not all bleeding is a period - ovulation spotting and irregular bleeding can be mistaken for one, timing sex at exactly the wrong moment. The honest odds: lowest of the cycle, but not zero, and "lowest" is not a contraceptive strategy - unplanned pregnancies from period sex happen regularly. If pregnancy is not the plan: use contraception regardless of cycle day, and if unprotected period sex just happened and pregnancy would be a problem, emergency contraception works within a few days - sooner is better. If pregnancy is the plan: the fertile window is the five days before ovulation plus the day itself, per the Office on Women's Health. Pymander, a free AI doctor available 24/7 by text, can help you think through the timing.