Period Tracker

It projects your next period by adding your average cycle length to your last period's start date, which assumes every cycle is identical — almost no one's actually are. Cycle length commonly varies by several days month to month due to stress, illness, travel, and other ordinary factors. If your period runs later than the estimate, the tracker tells you explicitly and by how many days, rather than continuing to count down. Accuracy improves the more cycles you track and enter.

It doesn't just add 14 days to your last period. It first projects your next period from your cycle length, then subtracts your luteal phase length (14 days by default) from that projected date. This is more reliable for cycles that aren't exactly 28 days, since the luteal phase (ovulation to next period) tends to stay more consistent than the days before ovulation.

The tracker flags this directly, showing how many days overdue you are. A single late or missed period is common and not usually a cause for concern — stress, illness, travel, and normal cycle variation can all delay it. That said, consider a pregnancy test if there's a chance you could be pregnant, and speak with a healthcare provider if you miss three or more cycles in a row.

Not meaningfully for ovulation or fertility-window purposes. Hormonal contraception (the pill, patch, or ring) suppresses natural ovulation, so any bleeding is withdrawal bleeding on a schedule set by your medication, not a natural cycle. The date math will still run, but the ovulation and fertile-window estimates won't reflect what's actually happening in your body.

ACOG treats the menstrual cycle as a health indicator worth monitoring, generally framing 21-35 days as the typical adult range, with 28 days as an average rather than a requirement. Occasional variation outside that range isn't automatically a problem, but a consistent pattern outside it — or periods lasting under 2 or over 7 days — is worth discussing with a healthcare provider, since it can reflect hormonal conditions like PCOS or thyroid issues.