Quick answer: If your last period started on 6 November 2026 and your cycle is 28 days, your next period is due on 4 December 2026; a 5-day period would end on 8 December.
How it's calculated
A cycle is counted from the first day of one period to the first day of the next. Each predicted period starts one cycle length after the previous one: next period = first day of last period + cycle length. It ends (period length − 1) days after it starts, since the first day counts as day 1.
The table also shows the likely ovulation day in each cycle, about 14 days before the period that follows it.
For your cycle length, use the average of your last few cycles. A cycle of 21 to 35 days with bleeding for 2 to 7 days is common in adults; teenagers' cycles can run up to 45 days. Periods that suddenly change, stop, or come more often than every 21 days are worth discussing with a doctor.
Worked examples
- Last period 6 November 2026, 28-day cycle, 5 days: next 4–8 December 2026
- Same start, 31-day cycle: 6 Nov + 31 = 7 December 2026
Frequently asked questions
How do I work out my cycle length?
Count the days from the first day of one period to the day before the next one starts. Average the last three to six cycles for a better prediction.
Is a late period always a sign of pregnancy?
No. Stress, illness, travel, weight change and some medicines can delay a period. If you might be pregnant, a home pregnancy test is reliable from the day your period was due.
What is a normal period length?
Bleeding usually lasts 2 to 7 days. Periods lasting longer than 7 days, or very heavy bleeding, are a reason to see a doctor.
What is a normal cycle length?
For adults, usually 21 to 35 days, counted from the first day of one period to the first day of the next. Teens' cycles can be longer and vary more.
Why does my period come at a different time each month?
A few days' change is common. Stress, illness, travel, weight changes and exercise can all shift it, mainly by moving the day you ovulate.
When should I see a doctor about my cycle?
If periods stop for 3 months, come closer than 21 days or further than 35 days apart, are very heavy or very painful, or if you could be pregnant.