Your next periods and fertile window, mapped.
Enter your last period and typical cycle length — get your next three periods, estimated ovulation day and fertile window. Computed on your device, never uploaded.
Map your cycle
The luteal phase does the math
Ovulation is estimated by counting back a fixed 14-day luteal phase from each predicted period — the phase after ovulation is far more consistent between women than the phase before it. The fertile window spans roughly 5 days before ovulation through 1 day after, reflecting sperm survival (up to 5 days) and egg viability (about 24 hours).
Calendar predictions are genuinely useful for planning, but they're estimates: stress, travel, illness and PCOS all shift ovulation. Consistently irregular cycles (varying by more than 7–9 days), very heavy bleeding, or cycles outside 21–35 days are each worth a gynecologist visit — not because they're emergencies, but because they're diagnosable and usually treatable.
These results are indicative wellness estimates based on standard published formulas — not a diagnosis or medical advice. Always consult your doctor for clinical decisions. Calendar methods are not reliable as sole contraception.
Frequently asked questions
It's an estimate — good for planning, weaker for precision. Ovulation kits (LH strips) and cycle-tracking with basal temperature are more accurate if you're actively trying to conceive.
If cycles are consistently shorter than 21 or longer than 35 days, vary by more than about 8 days, involve very heavy bleeding or severe pain, or if you've been trying to conceive for 12 months (6 if over 35).
Completely — this calculator runs in your browser only. No dates are transmitted, stored or shared with anyone, including us.
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