Period Calculator
Predict your next three period start dates from your cycle length.
Period Calculator
| Next period starts | January 29, 2026 |
| Following period starts | February 26, 2026 |
| Third period starts | March 26, 2026 |
From a last period of January 1, 2026 with a 28-day cycle, the next three periods are predicted to start January 29, February 26 and March 26, 2026.
This calculator projects your next three period start dates by adding your average cycle length to the first day of your last period, one cycle at a time. It is the same calendar method used by period-tracking apps.
Predictions assume your cycle stays at its average — stress, illness, travel and hormonal changes routinely shift real periods by several days. Educational use only; not a contraceptive method and not medical advice.
The formula
Worked example
From a last period of January 1, 2026 with a 28-day cycle, the next three periods are predicted to start January 29, February 26 and March 26, 2026.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
What is a normal cycle length?
Adult cycles typically run 21–35 days (24–38 by some clinical definitions), counted from the first day of one period to the first day of the next. Variation of a few days between cycles is normal.
How can I make predictions more accurate?
Average your last 6–12 cycle lengths rather than using a single cycle, and re-anchor the calculation each month with the actual start date.
Category: Health & Fitness calculators