BiteCheck calculators
Period Calculator
Estimate your next period, ovulation, and fertile window using your last period start date, cycle length, and period length.
How to use the period calculator
Enter the first day of your last period, your average cycle length, and how many days your period typically lasts. The calculator estimates your next period, your likely ovulation day, and the fertile window leading up to it.
Understanding your results
- Next period dates: Based on your cycle length, we project when your next period will start and end.
- Ovulation: Estimated 14 days before your next period, which is a common benchmark for many cycles.
- Fertility window: The 5 days before ovulation through the day after, when conception is most likely.
Tips for more accurate tracking
- Use the average of your last 3–6 cycles if your timing varies.
- Log your cycle in BiteCheck to spot patterns and plan ahead.
- If your cycle is irregular or changes suddenly, check in with a healthcare provider.
Frequently asked questions
How does the period calculator work?
We estimate your next period start by adding your cycle length to your last period start date, then calculate ovulation as 14 days before the next period.
What is the fertile window?
The fertile window includes the 5 days before ovulation plus the day of ovulation and the day after, when conception is most likely.
What if my cycle length changes?
If your cycle varies, use your recent average and update the calculator whenever your timing shifts to keep estimates accurate.
Is this calculator medical advice?
No. This tool provides estimates only. Talk to a healthcare professional for personalized fertility or menstrual guidance.
Informational only, not medical advice. Consult a healthcare professional for personalized guidance.
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