Pink Mom MathPeriod Prediction Calculator
Enter your recent period start dates to predict your next 6 months of periods on a scrollable calendar.
Add at least 3 period start dates to see your prediction.
How the Period Prediction Calculator Works
The calculator analyzes your entered period start dates to calculate your average cycle length. It then projects this pattern forward by 6 months, marking the predicted start dates and all period days on a calendar.
The Formula
Average cycle length = mean of all intervals between consecutive period start dates. Each predicted period starts at: last date + (average cycle length × period number).
Period Duration
The calendar highlights each predicted period start date plus your specified period duration (default 5 days). This gives you a visual overview of the days each month when you are likely to be menstruating.
Using This Calculator with PCOS and Irregular Cycles
Period predictions work best when your cycles are consistent. With PCOS or irregular cycles, the calculator can still provide useful estimates — but the uncertainty window around each predicted date will be wider, and that's completely normal.
The more cycle data you enter, the better the prediction becomes. With 3 cycles, the calculator captures a rough average. With 6–12 cycles, it captures your full range of variability and the prediction improves meaningfully. If your cycles vary significantly — say, between 25 and 40 days — the forecast will reflect that spread with a wider uncertainty band rather than a single precise date.
PCOS can cause some cycles to be unusually short (even just 21 days) and others to stretch past 60 days. When entering your dates, include all of these — even the outliers — because they represent your real pattern. Excluding very long or very short cycles gives a falsely precise picture of regularity you don't actually have.
One practical tip: track your actual period start dates on a calendar app alongside these predictions. Over time, you'll build a personal dataset that makes predictions more accurate. You can also use the Cycle Length Analyzer tool to see your consistency score and get a statistical view of how your cycle variability compares to what's typical for PCOS.
Frequently Asked Questions
Related Calculators
Cycle Length Analyzer
Analyze your cycle consistency with a 0–100 regularity score and detect irregularities from your period history.
Ovulation Calculator
Calculate your ovulation day and fertile window based on your cycle. Supports irregular cycles and PCOS mode.
Safe Days Calculator
Identify low-fertility days in your cycle using the calendar method. Educational use only — not reliable contraception.
Luteal Phase Calculator
Calculate your luteal phase length and compare to the normal 12–16 day range for cycle health.
BBT Ovulation Calculator
Detect ovulation from daily basal body temperature readings with a visual temperature chart and coverline.
Related Guides
PCOS and Fertility: What to Know About Irregular Cycles
How PCOS affects ovulation, cycle length, and conception. Learn strategies for tracking irregular cycles and when to seek fertility support for PCOS.
What Your Cycle Length Tells You About Your Health
A guide to interpreting your menstrual cycle length — what is normal, what signals irregularity, and how cycle patterns reflect hormonal and overall health.
Period Irregularity: When to See a Doctor
Know the difference between normal cycle variation and irregular periods that warrant medical attention. Covers missed periods, spotting, very short or long cycles, and red flags.
This calculator provides estimates for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health or your baby's health.
Period predictions are estimates based on historical cycle data and may not account for hormonal changes, stress, illness, or other factors affecting cycle regularity.