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Period Calculator

Predict your next periods, ovulation and fertile days.

Last updated: Free, no sign-up Private — runs in your browser

Quick answer: when is my next period?

Add your cycle length to the first day of your last period. With a 28-day cycle that began on 1 January, your next period is expected on Thursday, 29 January 2026.

Overview of the Period Calculator

The Period Calculator predicts when your next periods will start and end for the coming 12 cycles, along with the ovulation date and fertile window of each. Enter the first day of your last period, your usual cycle length, the number of days your period lasts and your luteal phase.

Cycles typically vary by a few days. A typical cycle is 21–35 days and a period lasts 2–7 days. Talk to a doctor if your periods are very irregular, very heavy or painful, or you miss several in a row. See the Ovulation Calculator, Conception Calculator and the Pregnancy Calculator.

How We Calculate

The calculator applies the standard published formulas step by step.

  1. Day 1 is the first day of bleeding.
  2. Next period start = last period start + cycle length; repeat for twelve cycles.
  3. Period end = start + period length − 1.
  4. Ovulation = start of the cycle + (cycle length − luteal phase).
  5. Fertile window = 5 days before ovulation to 1 day after.
next period = last period start + cycle length
Worked example — period calculator
ItemValue
Cycle length28 days
Period length5 days
Next periodThursday, 29 January 2026 – Monday, 2 February 2026
Ovulation before itThursday, 15 January 2026
Following ovulationThursday, 12 February 2026
Predicted periods for the next 12 cycles
CyclePeriod startsPeriod endsOvulationFertile window
1Thursday, 1 January 2026Monday, 5 January 2026Thursday, 15 January 2026Saturday, 10 January 2026 – Friday, 16 January 2026
2Thursday, 29 January 2026Monday, 2 February 2026Thursday, 12 February 2026Saturday, 7 February 2026 – Friday, 13 February 2026
3Thursday, 26 February 2026Monday, 2 March 2026Thursday, 12 March 2026Saturday, 7 March 2026 – Friday, 13 March 2026
4Thursday, 26 March 2026Monday, 30 March 2026Thursday, 9 April 2026Saturday, 4 April 2026 – Friday, 10 April 2026
5Thursday, 23 April 2026Monday, 27 April 2026Thursday, 7 May 2026Saturday, 2 May 2026 – Friday, 8 May 2026
6Thursday, 21 May 2026Monday, 25 May 2026Thursday, 4 June 2026Saturday, 30 May 2026 – Friday, 5 June 2026
7Thursday, 18 June 2026Monday, 22 June 2026Thursday, 2 July 2026Saturday, 27 June 2026 – Friday, 3 July 2026
8Thursday, 16 July 2026Monday, 20 July 2026Thursday, 30 July 2026Saturday, 25 July 2026 – Friday, 31 July 2026
9Thursday, 13 August 2026Monday, 17 August 2026Thursday, 27 August 2026Saturday, 22 August 2026 – Friday, 28 August 2026
10Thursday, 10 September 2026Monday, 14 September 2026Thursday, 24 September 2026Saturday, 19 September 2026 – Friday, 25 September 2026
11Thursday, 8 October 2026Monday, 12 October 2026Thursday, 22 October 2026Saturday, 17 October 2026 – Friday, 23 October 2026
12Thursday, 5 November 2026Monday, 9 November 2026Thursday, 19 November 2026Saturday, 14 November 2026 – Friday, 20 November 2026
Next period start by cycle length
CycleNext period
26-day cycleTuesday, 27 January 2026
28-day cycleThursday, 29 January 2026
30-day cycleSaturday, 31 January 2026
32-day cycleMonday, 2 February 2026
35-day cycleThursday, 5 February 2026

Period Calculator — Frequently Asked Questions

How do I calculate my next period?

Add your average cycle length to the first day of your last period.

What is a normal cycle length?

Between 21 and 35 days is typical for adults. Teens may have longer cycles.

How long should a period last?

Usually 2 to 7 days.

Why is my period late?

Stress, illness, weight change, hormonal conditions, breastfeeding and pregnancy are common reasons. If you may be pregnant, take a test.

When should I see a doctor?

If your periods stop for three months, come less than 21 or more than 35 days apart, are very heavy or painful, or you bleed between periods.

Can I rely on a calendar to avoid pregnancy?

No. Cycle length varies, so this tool is not a contraceptive method.

How is the period calculator calculated?

It uses the published formula: next period = last period start + cycle length The full method and a worked example are shown on this page.

Is this medical advice?

No. The calculator gives general estimates for information and education. It cannot diagnose or treat anything, so please speak to a doctor or qualified professional about your own health.

Can I use US or Indian units?

Yes. Choose centimetres or feet and inches for height, and kilograms, pounds or stone for weight; the results are converted for you.

Is my data stored?

No. Everything is calculated in your browser and nothing you enter is uploaded or saved.

More Free Calculators You May Need

Ovulation CalculatorPredict your ovulation day and fertile window for six cycles.Conception CalculatorEstimate when you are most likely to conceive and your possible due date.Pregnancy CalculatorFind your due date, current week and trimester dates.Due Date CalculatorEstimate your baby's due date from five different starting points.Pregnancy Conception CalculatorWork out when you probably conceived from your due date.Date CalculatorAdd or subtract days, months and years — or find the gap between two dates.

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