🩸 Period Calculator
Find out when your next period is due, plus your fertile days and ovulation dates for the next six cycles.
Quick answer: Your next period is expected to start on October 29, 2026 (in 18 days) and last until about November 2, 2026. Your estimated ovulation date is October 15, 2026, with a fertile window of Oct 10 – Oct 16.
Updated · Free · No sign-up · Works on any device
Period Calculator inputs
Result
Your next period starts
October 29, 2026
Expected to last Oct 29 – Nov 2 · in 18 days
- Ovulation (estimated)
- October 15, 2026
- Fertile window
- Oct 10 – Oct 16
- Period after that
- November 26, 2026
Calendar estimate only – not a method of contraception.
Your next 6 periods
| # | Period | Fertile window | Ovulation |
|---|---|---|---|
| 1 | October 29, 2026 (to Nov 2) | Oct 10 – Oct 16 | Oct 15 |
| 2 | November 26, 2026 (to Nov 30) | Nov 7 – Nov 13 | Nov 12 |
| 3 | December 24, 2026 (to Dec 28) | Dec 5 – Dec 11 | Dec 10 |
| 4 | January 21, 2027 (to Jan 25) | Jan 2 – Jan 8 | Jan 7 |
| 5 | February 18, 2027 (to Feb 22) | Jan 30 – Feb 5 | Feb 4 |
| 6 | March 18, 2027 (to Mar 22) | Feb 27 – Mar 5 | Mar 4 |
The fertile window and ovulation shown on each row are those of the cycle leading up to that period.
For general information only – not medical advice. Consult a healthcare professional.
How the period calculator works
Your cycle starts on the first day of bleeding. The calculator adds your average cycle length to find each future period, and counts back 14 days from each period to estimate ovulation – the luteal phase after ovulation is fairly constant for most people.
Next period = last period start + cycle length · Ovulation ≈ next period − 14 days
Fertile window = ovulation − 5 days … ovulation + 1 day
Worked example
Your last period began on October 1, 2026, your cycle is 28 days and your period lasts 5 days. The next period is due on October 29 (to November 2). Counting back 14 days, ovulation is around October 15 and the fertile window is October 10–16. The following periods fall on November 26, December 24, January 21, February 18 and March 18.
Next period by cycle length
| Cycle length | Next period (days after last start) | Ovulation (cycle day) |
|---|---|---|
| 24 days | 24 | Day 11 |
| 28 days | 28 | Day 15 |
| 30 days | 30 | Day 17 |
| 32 days | 32 | Day 19 |
| 35 days | 35 | Day 22 |
Tips for better predictions
- Log the first day of each period for a few months and enter your average cycle length.
- If you entered an older date, the calculator rolls forward to your current cycle automatically.
- See a doctor if cycles are shorter than 21 or longer than 35 days, very irregular, very heavy, or if periods stop for 3 months or more.
For general information only – not medical advice. Consult a healthcare professional.
Frequently asked questions
How do I calculate my next period?
Add your average cycle length to the first day of your last period. With a 28-day cycle and a period that started on October 1, the next one is due on October 29.
What is a normal cycle length?
Adult cycles typically last 21–35 days, counted from the first day of one period to the first day of the next, and periods usually last 2–7 days. Cycles in teenagers and around perimenopause vary more.
Why is my period late?
Stress, illness, travel, weight change, intense exercise, breastfeeding, some medicines and conditions such as PCOS or thyroid problems can delay a period. If you might be pregnant, take a pregnancy test.
How accurate is a period calculator?
It assumes every cycle has the same length, so it works best for regular cycles. Most people vary by a few days; use the average of your last three to six cycles for better predictions.
Can I use this to avoid pregnancy?
No. Calendar predictions are not reliable contraception, because ovulation can shift from cycle to cycle. Talk to a healthcare professional about effective methods.