Ovulation Calculator
Your fertile window is about six days long, ending on ovulation day. Find yours — and see the due date each cycle would bring.
21-45 days · count period day 1 to the day before the next period
Mostly 14 · leave as-is if unknown
Ovulation day varies cycle to cycle — stress, illness and travel all nudge it. Ovulation test strips and temperature tracking pinpoint it better than any calendar; treat this as your planning baseline.
How fertile windows work
Sperm survive up to five days inside you; the egg lives just 12-24 hours after release. That makes the six days ending on ovulation day your fertile window — with the two days before ovulation and ovulation day itself the statistically best to try.
We estimate ovulation as cycle length minus your luteal phase (14 days for most people), and project it across your next three cycles using your average length.
Questions people ask
When is the best day to try to conceive?
The two days before ovulation and ovulation day itself. Because sperm outlive the egg, being early beats being late — intercourse every 1-2 days across the fertile window covers it all.
How do I confirm ovulation actually happened?
Calendar math estimates it; ovulation test strips detect the LH surge that precedes it by about a day, and a sustained temperature rise of 0.5°F confirms it after the fact.
My cycles are irregular — is this still useful?
As a rough map only. With irregular cycles, test strips are more reliable, and a provider visit after 12 months of trying (6 months if over 35) is the standard next step.