Calculator
Ovulation Calculator
Estimate ovulation date, fertile window, next period, and test date from cycle length and luteal phase.
Last updated: August 21, 2026
How it works
Ovulation is estimated by subtracting the luteal-phase length from the expected next period date. The fertile window is shown from five days before ovulation through the day after.
Ovulation estimates use average cycle timing and may not predict ovulation accurately for irregular cycles, recent contraception changes, postpartum cycles, or medical conditions.
This tool is informational and does not replace medical advice, fertility diagnosis, contraception counseling, or care from a qualified clinician.
References
FAQ
How is ovulation estimated?
The calculator estimates the next period from your last period and cycle length, then subtracts the luteal phase to estimate ovulation.
Can this predict ovulation exactly?
No. Ovulation can shift because of stress, illness, irregular cycles, postpartum changes, medication, contraception changes, or health conditions.
What does fertile window mean?
It is an estimated range around ovulation when pregnancy is more likely, based on average cycle timing and sperm survival.
Should I use this for contraception?
No. Do not use this calculator as birth control or medical guidance. Speak with a qualified clinician for contraception or fertility advice.