Period calculator
When is my next period? Enter the first day of your last period and your usual cycle length to see your next six periods.
Runs in your browser. Nothing you type leaves this page.
Next period
Tuesday 3 November
in 14 days
| Period | Fertile window | Ovulation |
|---|---|---|
| 3–7 Nov | 15–21 Oct | 20 Oct |
| 1–5 Dec | 12–18 Nov | 17 Nov |
| 29 Dec 2026 – 2 Jan 2027 | 10–16 Dec | 15 Dec |
| 26–30 Jan | 7–13 Jan | 12 Jan |
| 23–27 Feb | 4–10 Feb | 9 Feb |
| 23–27 Mar | 4–10 Mar | 9 Mar |
An estimate, not medical advice. Do not use it as birth control.
How it works
Each period starts one cycle length after the one before, and ovulation is counted 14 days back from the next period. A typical cycle lasts 24 to 38 days, and only about one in eight is exactly 28 days, so treat each date as the middle of a range.
Sources: Office on Women's Health: Your menstrual cycle , Bull et al., npj Digital Medicine, 2019 (funded by Natural Cycles) , NHS: Fertility in the menstrual cycle
Questions
- How accurate is a period calculator?
- It assumes every cycle is the same length. Real cycles drift by a few days, so expect your period within a few days of each date, and less precisely the further out it is.
- What is a normal cycle length?
- A typical cycle lasts 24 to 38 days. Talk to a doctor if yours are often shorter or longer than that, or suddenly change.
- How does Vela predict periods?
- Vela learns from your own logged cycles on your iPhone and weights recent ones more, so its predictions sharpen as you log.
- Is anything I type saved?
- No. The calculation runs in your browser, and nothing you type is sent or stored.
Let your own cycles do the math
Vela learns your cycle from your own logs and keeps them on your iPhone. No account needed.
More calculators: Ovulation calculator Due date calculator