28 day cycle, 5 day period
- Expected end
- May 31, 2026
- Following period
- Jun 24, 2026
- Third period
- Jul 22, 2026
Period Calculator
Use this free period calculator to estimate the next period start, expected end, and upcoming cycle dates.
Research-based formula Estimate limits shown Examples included Private history
Formula steps
- Start from the first day of the last period.
- Add cycle length until the next predicted start date is in the future.
- Use period length to estimate the expected end date.
How to use the period calculator
- Enter the requested measurements, dates, lab values, or workout details.
- Check that the units and formula assumptions match what the tool is asking for.
- Press the calculate button to see the answer, supporting metrics, and formula steps.
- Read the estimate with the health disclaimer in mind, then copy the result if you need it for notes.
Common uses
Estimate the next period start date.
Estimate expected period end date.
List upcoming cycles for planning.
Use calendar estimates while remembering cycles can change.
Examples
Next period estimate
Next cycle dates
Earlier next period estimate
Frequently asked questions
Quick answers about formulas, inputs, estimate limits, professional guidance, examples, and private in-browser history.
What can I use the Period Calculator for?
Use it for quick educational estimates, planning, comparison, and trend checks. Health and fitness results should be interpreted with context, not as a diagnosis.
How does the Period Calculator calculate the result?
The calculator adds cycle length to the first day of the last period until it finds the next expected period start date.
Is this medical advice?
No. This page provides an educational estimate only. Talk with a qualified health professional before making medical, pregnancy, nutrition, medication, or safety decisions.
Are my health inputs private?
Yes. The calculator runs in your browser tab. Recent answers stay only on the page while you use it and are not sent to a server.