About Period Tools
A small independent team building tools we want to use ourselves — clean, accurate, and respectful of your time.
Why we built it
We kept opening Google to answer the same simple questions about our cycles — when’s my next period, am I in my fertile window, how late am I — and getting served clunky brand calculators that wouldn’t work on a phone, blog posts that buried the answer under 2,000 words of stock-photo filler, or apps that wanted our data first.
We wanted a place that just worked. So we made one. Open the page, pick a date, see your answer. No signup, no login, no tracking pixel sending your cycle dates to ad networks. Everything runs in your browser. We don’t see your dates and we can’t — there’s nowhere on our server for them to go.
What we’re careful about
- Accuracy. The math behind every calculator on this site is the same standard method your healthcare provider uses — Naegele’s rule for due dates, the luteal-phase ovulation estimate, ABO/Rh genetics for blood type (the Chinese gender chart is clearly labelled fun-only). It’s tested.
- Mobile first. Most people search these terms on a phone. Every screen, every input, every output is designed for a small screen first.
- Honest framing. A calculator is an estimate. We say so. The folklore tools are clearly labelled as folklore. Anything that could mislead about a real health decision gets a disclaimer.
- No dark patterns. No fake countdown timers, no fake low-stock warnings, no aggressive pop-ups, no signup walls in front of free tools.
How we keep the lights on
Period Tools is supported by advertising (the standard kind shown by networks such as Google AdSense). In the future we may also add a small number of affiliate links to apps and products we genuinely think are helpful — and if we do, we’ll always say so clearly and never let a sponsor decide our content. For now, ads are how we keep the lights on.
What we don’t do: collect your cycle data, sell it, share it with anyone, or store it anywhere. The calculators are client-side — your inputs never leave your browser.
Who’s behind Period Tools?
A small independent team focused on health-adjacent calculators and reference tools. We don’t list individual names — not because we’re hiding, but because every page is shipped by the team, not a single author, and the work compounds when one person isn’t a single point of failure.
If you have a question, a correction, or just want to tell us something we got wrong, we genuinely want to hear it. Reach out via our contact page.