1. How accurate is this calculator?

While our tool uses standard biological formulas, every body is unique. Stress, diet, and sleep can shift your cycle. Think of this as a very reliable "weather forecast" for your body—great for planning, but keep a spare pad in your bag just in case!

2. How do I accurately identify the start of a new menstrual cycle?

The very first day you notice actual blood flow (not just spotting) is officially Day 1. That is the date you should enter into the "Last Period Start" field for the most accurate results.

3. My cycle length changes every month. What should I do?

Don't sweat it—irregularity is common. Add up the days of your last three cycles and divide by three to find your average. Use that average number on the slider for the best prediction.

4. Can I use this for birth control?

This period calculator is for educational and planning purposes only. Because ovulation can shift unexpectedly, it should not be used as your primary method of pregnancy prevention.

5. Why is the fertile window 6 days long?

Even though an egg only lives for about 12-24 hours, sperm can survive inside the body for up to 5 days. This means the "danger zone" (or opportunity zone!) starts several days before you actually ovulate.