Comprehensive Calculator Guide
This calculator predicts your next three periods, when the next one should end and your approximate ovulation day, from the first day of your last period and your usual cycle length. With a last period on 1 October 2026 and a 28-day cycle, the next is due on Thursday 29 October.
Cycle length and ovulation
A cycle runs from the first day of one period to the day before the next. 28 days is a common average, and roughly 21 to 35 days is normal for adults. Ovulation usually happens about 14 days before the next period, so in a 32-day cycle it falls around day 18.
See a doctor if your cycles are regularly shorter than 21 or longer than 35 days, or come with very heavy bleeding, severe pain or bleeding between periods. These dates are estimates and must not be used as contraception.
How to Use
- 01Pick the first day of your last period.
- 02Enter your cycle and period length, or keep 28 and 5.
- 03Read the next periods and the approximate ovulation day.
Formula Used
Next period = last period + cycle length | Ovulation ≈ next period − 14 daysPractical Examples
Example 1: a 28-day cycle
From 1 October 2026: 29 October, then 26 November and 24 December; ovulation around 15 October.
Example 2: a 32-day cycle
From 1 October 2026: 2 November, then 4 December and 5 January 2027; ovulation around 19 October.
Important Tips
- Log the first day of each period to learn your real cycle length.
Common Mistakes to Avoid
- Counting from the last day of bleeding.
- Assuming ovulation is always on day 14.
Frequently Asked Questions
- How do I work out my next period?
- Add your cycle length to the first day of your last period.
- What is a normal cycle length?
- Roughly 21 to 35 days for adults.
- Can I use this as contraception?
- No.