Period Calculator: Next Date and Six-Cycle Calendar
Project upcoming period dates from your last start date and average cycle length. See a calendar estimate without false ovulation certainty.
Your inputs
Choose the units and assumptions that match your data. Example inputs are illustrative.
Your result
Enter your values, then choose Calculate.
Results are calculated in your browser. Display rounding does not change the underlying calculation.
Calculation breakdown
Method, assumptions and worked example
How it works
The next estimated start is the last period start plus average cycle length. Each later cycle adds the same number of days. The estimated last bleeding day is start + bleeding duration − 1. Cycle length runs from one period’s first day to the next period’s first day.
Worked example
Starting 1 October 2026 with a 28-day cycle gives an estimated next start of 29 October. Five bleeding days would extend through 2 November.
Using the result
Real cycles vary. Stress, illness, contraception and life stage may change timing. Date projections neither confirm ovulation nor identify safe days for avoiding pregnancy. For an unexpectedly missed period when pregnancy is possible, use an appropriate pregnancy test and seek advice as needed.
Frequently asked questions
Can I use this as contraception?
No. A calendar average cannot identify reliably safe days.
What if my cycles are irregular?
The output can be substantially wrong; use your actual tracking history and professional advice rather than relying on a single average.
Method review and references
Formula and content reviewed on 10 October 2026. Worked examples are hypothetical. Methods and assumptions are explained on each page. Health estimates are not clinical measurements; symbolic tools are for entertainment.