Period calendar
Enter when your last period started and how long your cycle runs. You get the dates of the coming cycles, the day you are on now, and which phase that falls in.
- Days until then
- 14 days
- Day of your cycle today
- 15
- Phase you are in
- Ovulatory
- Cycle length used
- 28 days
- Period length used
- 5 days
| Cycle | Period | Ovulation | Fertile window |
|---|---|---|---|
| 1 | November 4, 2026 → November 8, 2026 | November 18, 2026 | November 13, 2026 → November 19, 2026 |
| 2 | December 2, 2026 → December 6, 2026 | December 16, 2026 | December 11, 2026 → December 17, 2026 |
| 3 | December 30, 2026 → January 3, 2027 | January 13, 2027 | January 8, 2027 → January 14, 2027 |
| 4 | January 27, 2027 → January 31, 2027 | February 10, 2027 | February 5, 2027 → February 11, 2027 |
| 5 | February 24, 2027 → February 28, 2027 | March 10, 2027 | March 5, 2027 → March 11, 2027 |
| 6 | March 24, 2027 → March 28, 2027 | April 7, 2027 | April 2, 2027 → April 8, 2027 |
A projection for a regular cycle, not a medical assessment or a contraceptive method. Cycles shift for many reasons; persistent changes are worth raising with a clinician.
The formula
Each cycle starts one cycle length after the last. Ovulation is placed 14 days before the next expected period, and the fertile window runs from five days before ovulation to one day after.
Worked example
With a 28-day cycle starting 1 October, the next periods begin on 29 October, 26 November and 24 December, with ovulation on the 15th of each cycle.
How to use it
- 1Count day one as the first day of real bleeding, not spotting.
- 2If your cycles vary, use your average over the last three to six months.
- 3Read the later cycles as increasingly rough — small variations compound the further out you project.
Questions people ask
My cycle is never the same length. Is this any use?
As a rough guide, yes, but read the window rather than the date. If your cycles vary by more than about seven days, tracking your actual start dates over a few months will tell you more than any projection.
What are the four phases?
Menstrual is the bleeding itself. Follicular runs from then until ovulation, as an egg matures. Ovulatory is the release. Luteal is the roughly fortnight-long stretch before the next period, and it is the steadiest part of the cycle.
Last reviewed: 2026-10-20