How I Built a Simple Ovulation Calculator Using HTML, CSS, and JavaScript

How I Built a Simple Ovulation Calculator Using HTML, CSS, and JavaScript I’ve been building small, free online tools as part of my website, and recently I built an Ovulation Calculator that predicts the fertile window and next period date based on cycle data. You can try it here: 👉 https://www.civvy.tech/health-tools/ovulation-calculator This post is a short breakdown of how I built it. The Idea Many ovulation calculators online are cluttered, require login, or are full of ads. I wanted to build something that is: Fast Private (no login) Mobile friendly Simple UI Instant calculation So I built a lightweight calculator using just HTML, CSS, and vanilla JavaScript . How the Calculation Works The logic is actually simple. Most people ovulate 12–16 days before the next period , not exactly in the middle of the cycle. So the formula I used: Ovulation Day = Cycle Length − Luteal Phase Length Then: Fertile Window Start = Ovulation Date − 5 days Fertile Window End = Ovulation Date + 1 day Nex