Sperm usually survive for two to three days, although they can live for up to five days. If your cycle is regularly 28 days, then you must usually ovulate around day 14 (as confirmed by ovulation tests in the past). However, this doesn’t mean that you will always ovulate on day 14. Our bodies are unpredictable, which is why natural family planning isn’t totally reliable, even for women whose cycles are usually as regular as clockwork. If you only had unprotected intercourse on day 6, then you probably ovulated around day 8 or 9 to become pregnant. So, if you hadn’t conceived, your period would have been early (around day 22 or 23 instead of day 28). Of course, there is no way of knowing for sure when you ovulated, and your partner’s sperm may survive longer than the average.