Enter the first day of your last period and your cycle length to predict your next period, estimated ovulation, and fertile window.
Estimates only.
This calculator uses the standard Naegele-style cycle model: your next period starts one full cycle after the first day of your last period. Ovulation typically falls about 14 days before your next period, and the fertile window spans roughly 6 days ending on ovulation day.
Cycle lengths vary naturally from person to person and month to month. Stress, illness, travel, and hormonal changes can all shift your cycle. These dates are general estimates based on an assumed regular cycle. They are not medical advice. If you have concerns about irregular periods or fertility, consult your doctor or midwife. An ultrasound or hormone panel is the clinical standard for cycle and ovulation assessment.
Note: The period length input is noted for future tracking use and does not change the predicted dates above, which depend on cycle length only.
Add your cycle length (typically 28 days) to the first day of your last period. For example, if your last period started January 1 and your cycle is 28 days, your next period is predicted around January 29. These are estimates only. Confirm patterns with your doctor if needed.
Count from the first day of one period to the first day of the next. Track 3 or more cycles and average them for a more reliable number. A typical cycle ranges from 21 to 35 days; 28 days is the textbook average.
Compare today's date to the predicted start date for your current cycle. A period is generally considered late if it has not arrived within 5 or more days of the expected date. Occasional variation of a few days is normal. If your period is significantly late, take a pregnancy test and speak with a doctor.
It provides general estimates based on a regular cycle model. Real cycles vary due to stress, illness, age, and hormonal factors. This tool is not a substitute for medical advice. Always confirm important dates with your doctor or midwife.