" your fertile days are the five days before ovulation (because that’s how long sperm survive), and the one day after ovulation (because that’s how long the egg survives). After ovulation, you have a short 24-hour window to ovulate once more, and maybe conceive twins. Your egg(s) survive for another 24 hours, and then you cannot ovulate again for the rest of that cycle. "

― Lara Briden , Period Repair Manual