Ovulation to Period Date Calculator
From your ovulation date and luteal-phase length, find when your next period is due, the implantation window, and the earliest reliable test day.
How it works
period date = ovulation + luteal-phase length · implantation window = ovulation + 6 to 12 days
The luteal phase — from ovulation to the next period — is the most stable part of the cycle, typically 12 to 16 days for a given person. Adding it to your ovulation date predicts the next period more reliably than counting forward from the last one, because ovulation timing varies more than the luteal length. Implantation, if conception occurs, usually happens 6 to 12 days after ovulation, and a home test becomes reliable around the day the period is due.
Worked example
Ovulation on September 10, 2026 with a 14-day luteal phase puts the next period on September 24. Implantation would fall between September 16 and 22, and a test is reliable from about September 24.
Frequently asked questions
Why count from ovulation instead of my last period?
The luteal phase is fairly fixed, so ovulation-to-period is stable. The follicular phase (period to ovulation) varies a lot, so counting forward from the last period is less accurate if your ovulation day shifts.
What luteal length should I use?
If you have tracked it, use your own — most people are 12 to 16 days. Fourteen is a common default. A luteal phase shorter than about 10 days is worth discussing with a clinician.
When can I test for pregnancy?
A test is most reliable from the day your period is due. Testing earlier risks a false negative because hCG may still be too low to detect.
Related calculators
Educational estimate — cycles vary; not a substitute for medical or contraceptive advice.