Period Tools Reviews — Discover what people think of this product.

Period Tools is a free, mobile-first period calculator.

What it does: enter your last period start date and average cycle length — get your next 6 period dates, your ovulation day and your most fertile window instantly.

Privacy-first: everything is computed in your browser. No account, no data stored, no tracking of your cycle history.

Also included: plain-language guides to cycle phases, irregular cycles, and how the fertile-window math works, so you understand the prediction instead of just trusting a number.

Free forever, works on any phone.