Period calendar estimate
Enter the first day of your last period and your cycle. The tool estimates the next 6.
General information, not medical advice. This result does not replace a doctor. If in doubt or if you have symptoms, see a health professional.
Result
Oct 18, 2026Next period estimated on
- 1: Oct 18, 2026 to Oct 22, 2026 (± 2 d)
- 2: Nov 15, 2026 to Nov 19, 2026 (± 3 d)
- 3: Dec 13, 2026 to Dec 17, 2026 (± 3 d)
- 4: Jan 10, 2027 to Jan 14, 2027 (± 4 d)
- 5: Feb 7, 2027 to Feb 11, 2027 (± 4 d)
- 6: Mar 7, 2027 to Mar 11, 2027 (± 5 d)
- Dates are computed in your browser and never saved. This is not contraception.
Inputs
- First day of last period
- 2026-09-20
- Cycle length
- 28
- Usual variation
- 2
- Period length
- 5
How it is calculated
Start number k = last period + k × cycle length.
Result
Next period estimated on
How it is calculated
- Start number k = last period + k × cycle length.
- End = start + period length − 1 day.
- The margin grows over time: ± variation × √k, rounded to a day.
Example
Period on 20 September 2026, 28-day cycle: next period around 18 October, then 15 November.
Good to know
- Real cycles change: far-off dates are less certain.
- This calendar is not a method of contraception.
- Very irregular, missing or painful periods are worth a medical opinion.
Frequently asked questions
What is this tool used for?
Enter the first day of your last period and your cycle. The tool estimates the next 6.
How is the result calculated?
Start number k = last period + k × cycle length.
What should I check before using the result?
Real cycles change: far-off dates are less certain.