Our period calculator is approximately 95% accurate for women with regular cycles. Accuracy depends on the regularity of your menstrual cycle and the correctness of the information you provide. For irregular cycles, predictions may be less accurate.

If your cycle length varies, use an average of your last 3-6 cycles for best results. The more irregular your cycles, the less accurate predictions will be. Consider tracking additional symptoms like basal body temperature for better accuracy.

This calculator is not a reliable form of birth control. While it can predict fertility windows, ovulation can vary unexpectedly. Always consult with a healthcare provider about contraceptive methods.