The short answer
Whether your period lasts 3, 5 or 7 days, ovulation usually happens about 14 days before your next period starts. Period length tells you how long bleeding lasts; cycle length — the days from the first day of one period to the first day of the next — tells you when ovulation is likely.
| Cycle length | Ovulation (approx.) | Days after a 5-day period ends | Days after a 7-day period ends |
|---|---|---|---|
| 24 days | Day 10 | 5 | 3 |
| 26 days | Day 12 | 7 | 5 |
| 28 days | Day 14 | 9 | 7 |
| 30 days | Day 16 | 11 | 9 |
| 32 days | Day 18 | 13 | 11 |
Counting starts with day 1 as the first day of bleeding. Notice how a long period combined with a short cycle can bring ovulation within just a few days of bleeding stopping.
Why period length doesn’t matter for ovulation
Your period is the shedding of the uterine lining from the last cycle. Meanwhile, in the ovary, a new egg-containing follicle has already started to grow. The time that follicle takes to mature is what varies — and it is the same process whether bleeding lasts three days or seven. After ovulation, the luteal phase lasts a fairly steady 12–14 days until the next period.
What period length can tell you
A period of 2 to 7 days is common. Very short, very long or very heavy periods, bleeding between periods, or a sudden change in your usual pattern are worth discussing with a doctor or nurse, as they can occasionally point to hormonal or other conditions.
Enter the first day of your last period, your cycle length and how many days your period lasts above to see every phase of your cycle, or use the Ovulation Calculator for your fertile window over the next three cycles.