Period Calculator
Project your next several periods and cycle phases from your history.
Inputs
Next period starts
Jul 29, 2025
Next period ends
Aug 2, 2025
Cycle length
28days
Period duration
5days
Step by step
LMP
= Jul 1, 2025
Cycle length
= 28 days
Next period
= Jul 29, 2025 – Aug 2, 2025
Projected periods
| # | Period starts | Period ends | Ovulation | Fertile from |
|---|---|---|---|---|
| 1.00 | Jul 29, 2025 | Aug 2, 2025 | Aug 12, 2025 | Aug 7, 2025 |
| 2.00 | Aug 26, 2025 | Aug 30, 2025 | Sep 9, 2025 | Sep 4, 2025 |
| 3.00 | Sep 23, 2025 | Sep 27, 2025 | Oct 7, 2025 | Oct 2, 2025 |
| 4.00 | Oct 21, 2025 | Oct 25, 2025 | Nov 4, 2025 | Oct 30, 2025 |
| 5.00 | Nov 18, 2025 | Nov 22, 2025 | Dec 2, 2025 | Nov 27, 2025 |
| 6.00 | Dec 16, 2025 | Dec 20, 2025 | Dec 30, 2025 | Dec 25, 2025 |
How it works
A menstrual cycle begins on the first day of bleeding and ends the day before the next period. Tracking your average cycle length lets you project future periods and fertile windows, which is useful for planning, recognising late periods, or identifying cycle irregularities.
Formula
Next period
Next period start = LMP + cycle length
This calculator is an estimate based on average cycle patterns. It is not a reliable contraceptive method. Consult a healthcare provider for personalised reproductive health advice.
Frequently Asked Questions
What is a normal cycle length?
A typical menstrual cycle is 24–38 days, with 28 days being the textbook average. Cycles shorter than 21 days or longer than 45 days may warrant investigation by a healthcare provider.
Why is my period late?
Many factors can shift ovulation — and therefore the next period — including stress, illness, significant weight change, intensive exercise, travel, hormonal contraceptives, or pregnancy. One late period is rarely cause for alarm, but a consistent pattern of irregular cycles is worth discussing with a doctor.
How do I use this for family planning?
This calculator can help you identify fertile windows for conception or, if combined with OPKs and BBT charting, as part of fertility awareness-based methods for avoiding pregnancy. Calendar methods alone have a higher failure rate than hormonal contraceptives.