Estimate your fertile window and ovulation day from your last period and average cycle length.
It uses the two numbers a cycle is built from — the first day of your last period and how many days your cycle usually lasts — to work out where ovulation and your fertile window likely fall this cycle, plus your next few expected period dates.
The Ovulation Tracker is built for people trying to conceive, and shows more than most people need for that. If you only want to know when your next period is due — or whether it's late — the dedicated Period Calculator is a faster, simpler tool for that.
Ovulation is when an egg is released, roughly in the middle of your cycle; implantation happens later, when a fertilized egg attaches to the uterine lining, typically 6–12 days after ovulation. Some people notice light "implantation bleeding" around then — the Implantation Calculator estimates that window from your ovulation date.
14 days is a typical average and a reasonable default if you've never tracked it. If you chart basal body temperature or use ovulation tests over a cycle or two, you can count backward from your period to your confirmed ovulation day for a more personal number.