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Reference table

Ovulation Table: Estimated ovulation day by Average cycle length

Reference table of estimated ovulation day for Ovulation across a range of average cycle length values — exact, engine-computed figures you can read off at a glance.

By Dr. Neha Sharma, MBBS, MD (Nutrition) · Updated Jun 2026 · 1 min read

This ovulation reference table shows the estimated ovulation day for a range of average cycle length values, assuming a first day of last period of 2025-01-01. Every figure is computed with the same engine that powers our Ovulation Calculator, so the numbers are exact.

Average cycle lengthEstimated ovulation dayFertile window startsFertile window ends
20 days07 Jan 202502 Jan 202508 Jan 2025
21 days08 Jan 202503 Jan 202509 Jan 2025
28 days15 Jan 202510 Jan 202516 Jan 2025
42 days29 Jan 202524 Jan 202530 Jan 2025
45 days01 Feb 202527 Jan 202502 Feb 2025

How to use this table

Find the row closest to your average cycle length and read across to the estimated ovulation day. For a value between two rows, the real figure sits between them — or enter your exact numbers in the Ovulation Calculator for a precise answer.

Need a value that is not in the table? — the Ovulation Calculator does it instantly, for free, with the formula and a worked example built in.

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Calculators in this guide

Frequently asked questions

Each cell is computed with the standard formula using exact arithmetic — the same calculation behind our Ovulation Calculator — so every figure is accurate for the stated assumptions.

Yes. The table covers common average cycle length values; for any exact figure, enter your own numbers in the Ovulation Calculator.

Dr. Neha Sharma · MBBS, MD (Nutrition)

Dr. Neha Sharma is a physician specialising in nutrition and preventive health, with over a decade of clinical experience helping patients understand body metrics and healthy lifestyle targets.