Period & Ovulation Forecast Calculator

Enter your average cycle length, period length and the first day of your last period; the tool forecasts the next 6 periods, ovulation windows and safe-day hints, and renders a highlighted 3-month calendar. All computing stays in your browser.

Average cycle

Period length

Last period start

Next 3 months (red = period, blue = ovulation window)

2026-10

Sun	Mon	Tue	Wed	Thu	Fri	Sat
				1	2	3
4	5	6	7	8	9	10
11	12	13	14	15	16	17
18	19	20	21	22	23	24
25	26	27	28	29	30	31

2026-11

Sun	Mon	Tue	Wed	Thu	Fri	Sat
1	2	3	4	5	6	7
8	9	10	11	12	13	14
15	16	17	18	19	20	21
22	23	24	25	26	27	28
29	30

2026-12

Sun	Mon	Tue	Wed	Thu	Fri	Sat
		1	2	3	4	5
6	7	8	9	10	11	12
13	14	15	16	17	18	19
20	21	22	23	24	25	26
27	28	29	30	31

Estimates only — not contraception or pregnancy-planning medical advice. If your cycle is clearly abnormal, see a doctor.

Result

Your cycle forecast will appear here.

Recent Records

No records yet

What is it

A typical menstrual cycle lasts 21–35 days, and ovulation usually happens about 14 days before the next period. Enter your own pattern to forecast upcoming periods and ovulation.

Notes & fun facts

Whether planning a pregnancy or just understanding your body, a forecast calendar helps you plan ahead — but cycles shift with stress and routine, so treat estimates as informational only.

Origin & history

Humans have long observed the menstrual cycle: medical research confirms that ovulation usually occurs about 14 days before the next period, with a fairly fixed luteal phase and a more variable follicular phase. On this basis, the calendar rhythm method has long been used to estimate periods and the fertile window, and modern women’s-health apps build their predictions on the same principle — estimates are for reference only.