Period Cycle Predictor

📖 Tool Introduction

Period Cycle Predictor is a free online tool that helps you see your own cycle pattern at a glance. It uses the common simplified model: a 28-day cycle and a 5-day period by default, with ovulation roughly fourteen days before the next period and a fertile window running from five days before ovulation to one day after. You simply enter your own cycle length, the number of period days, and the start date of your last period; the tool then works out when your next period is expected to begin, which day ovulation falls on, and which days make up the fertile window. It marks all of this directly on a six-week calendar: pink cells are period days, yellow cells are fertile days, the purple-outlined cell is ovulation day, and green cells are relatively safe days. Three summary chips at the top repeat the key dates in large numbers so you can grasp them instantly. It is important to understand that this tool only performs a mathematical calculation from the cycle length you provide; real ovulation is affected by sleep, stress, illness and many other factors, so results vary from person to person and are for reference only. They must not be used for contraception or medical diagnosis. Every calculation runs locally in your browser, and no health data is ever collected or uploaded. The color coding is designed to be read at a glance on a phone screen: pink reminds you to plan ahead, yellow and purple flag the days when a predicted cycle shift matters most, and green simply marks the rest. Because the model assumes a regular cycle, it works best as a planning companion for scheduling trips, strenuous exercise or a pre-emptive doctor visit, rather than as a source of certainty. Keeping the disclaimer visible at the bottom is intentional, so the page never quietly implies that the dates are guaranteed.

✨ Key Features

• Custom parameters: cycle length defaults to 28 days and period to 5 days, both adjustable
• Three predictions: next period start, ovulation day and fertile window are calculated automatically
• Calendar marks: a six-week calendar uses four colors for period, fertile, ovulation and safe days
• Summary chips: three top chips highlight key dates; today's cell gets an outline
• Copy result: the prediction summary can be copied in one click for your own notes
• Fully local: all math runs in the browser and no health data is uploaded

📝 How to Use

1. Type your average cycle length in days; the default is 28
2. Type how many days each period lasts; the default is 5
3. Pick the start date of your last period in the date picker
4. Click Predict and read the summary chips together with the calendar marks
5. Use the calendar to plan travel, exercise or doctor visits ahead; treat results as reference

⚠️ Notes

• Reference only: results are mathematical estimates; real ovulation varies by many factors
• Not contraception: this tool must not be used as birth control; safe days are never truly safe
• Valid ranges: cycle length should be 15-60 days and period days 2-10
• Health advice: for irregular cycles or pain, consult a qualified doctor
• Privacy: data is processed locally and never uploaded to any server