Free tool
Period / menstrual cycle calculator
Enter the first day of your last period, your average cycle length and average period length. The tool predicts your next 6 period dates, plus the estimated fertile window and ovulation day for each cycle. Nothing you type is stored or sent anywhere.
Your next period
This is a general estimate from a standard cycle-length calculation, not medical advice and not a diagnosis. Real cycles vary month to month, and this tool cannot know what is actually happening in your body. Consult a doctor for anything beyond general planning, including missed periods, irregular cycles, or symptoms that concern you.
Your next 6 predicted cycles
Each row assumes every future cycle matches the average length you entered above. Accuracy drops the further out the prediction goes.
| Cycle | Predicted period | Estimated ovulation | Estimated fertile window |
|---|---|---|---|
| 1 | - | - | - |
| 2 | - | - | - |
| 3 | - | - | - |
| 4 | - | - | - |
| 5 | - | - | - |
| 6 | - | - | - |
Common questions
How does this period calculator predict my next dates?
It starts from the first day of your last period and adds your average cycle length, once for each of the next 6 cycles. Cycle length is the number of days from the first day of one period to the first day of the next, so period 1 is your last period date plus one cycle, period 2 is period 1 plus another cycle, and so on.
How accurate are the later predictions, 3 to 6 months out?
Less accurate the further out they go. The calculator assumes every future cycle matches the average length you entered, but real cycles shift with stress, travel, illness, and other factors. Treat dates 3 to 6 cycles out as a rough calendar guide, and use the most recent actual period to re-run the estimate closer to the time.
What is the fertile window shown for each predicted cycle?
For each predicted cycle, the fertile window runs from 5 days before that cycle’s estimated ovulation day through 1 day after it. Sperm can survive in the body for up to about 5 days, and the egg is typically viable for about 24 hours after release, so the days leading up to ovulation carry the highest chance of conception, not just the day itself.
Does an irregular cycle affect these predictions?
Yes, significantly. This method assumes a fairly consistent cycle length and a roughly 14-day gap between ovulation and the next period. If your cycles vary by more than a few days month to month, if periods have stopped, or if you notice unusually heavy bleeding or severe pain, these are questions for a doctor, not something this calculator can assess.
Run a clinic or diagnostic lab?
Patients tracking their cycle end up at your lab for hormone panels. Their reports deserve to look this instant
- Hormone and PCOS work-up reports (TSH, prolactin, AMH and related tests) go out on your lab’s own branded report, with reference ranges and Low / Normal / High flags applied automatically.
- Delivered straight to the patient on WhatsApp, from your own branded number, white-labelled and QR-verified.
- Every referring gynaecologist’s commission is worked out automatically and totalled in one Pay-Run, alongside the patient’s full visit and report history.
See how reports reach the patient on the WhatsApp report delivery page →
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