Enter your last period start date and cycle length (typically 21–35 days; 28 is average). The calculator adds your cycle length to find the next period date. Ovulation is estimated as the midpoint of the cycle, and the fertile window spans 5 days before to 1 day after ovulation. Six future cycles are projected by adding multiples of your cycle length. The model assumes regular, predictable cycles and does not account for natural variation, stress, or hormonal changes.
This calendar method is rough; it works well for regular 28-day cycles but becomes less accurate with irregular cycles. For fertility tracking, consider ovulation predictor kits or basal body temperature charting.
No. This calendar method is NOT a reliable form of contraception. Modern contraceptives (hormonal, barrier, or IUD methods) are much more effective. Consult a healthcare provider.
Cycle length varies by up to 7 days in many people. If yours varies more, predictions become less reliable. Track 3–6 months to find your average, or use more precise methods (ovulation predictor kits, ultrasound).
The typical range is 21–35 days from the first day of one period to the first day of the next. 28 days is the population average, but 24–32 days is common.
Yes. Stress, illness, exercise intensity, weight changes, and travel can shift ovulation timing by several days. This calculator cannot predict those shifts.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.