Period Calculator
Calculate your next period date and ovulation.
Cycle Information
Please enter the first day of your last period
Next Cycle
Enter your cycle information to calculate next period
About This Calculator
The Period Calculator helps you predict your next menstrual period, ovulation date, and plan ahead for your menstrual cycle. Understanding your cycle pattern helps with planning and fertility awareness.
The calculator uses your last period date, average cycle length, and period duration to estimate upcoming cycle dates. Regular cycles make predictions more accurate, while irregular cycles may require tracking over several months for better estimates.
Formula & Calculation Method
Period Calculation:
Next Period Start = Last Period + Cycle Length
Next Period End = Next Period Start + Period Length - 1
Next Ovulation = Next Period Start - 14 days
Cycle Length = Days from period start to next period start
Menstrual cycles typically last 21-35 days, with 28 days being average. The period (menstruation) usually lasts 3-7 days. Ovulation typically occurs about 14 days before the next period, though this can vary based on cycle length.
How to Use This Calculator
- Enter Last Period: Input the first day of your last menstrual period.
- Enter Cycle Length: Input your average cycle length in days (typically 21-35 days).
- Enter Period Length: Input how many days your period usually lasts (typically 3-7 days).
- View Results: See your next period dates, ovulation date, and upcoming cycle predictions.
Frequently Asked Questions
How accurate are period predictions?
Accuracy depends on cycle regularity. If your cycles are regular (vary by 1-2 days), predictions are quite accurate. Irregular cycles make predictions less reliable. Tracking your cycle for 3-6 months improves accuracy.
What if my cycle is irregular?
Irregular cycles can make predictions challenging. Track your cycle for several months to identify patterns. If cycles vary significantly (more than 7-9 days), consider consulting a healthcare provider as it may indicate underlying issues.
Can stress affect my period?
Yes, stress, illness, travel, changes in routine, and other factors can affect cycle timing. The calculator provides estimates based on your average cycle, but actual dates may vary due to these factors.
How do I track my cycle length?
Mark the first day of your period (day 1) and count days until the next period starts. Track for 3-6 months and calculate the average. Many apps can help track cycles automatically.
Calculator by
NumCalculators Editorial Team
Multi-disciplinary Expert Team