Mother's age at her first period. Pediatric and epidemiological studies consistently find that mother's menarche age is the single strongest family predictor of a daughter's first period. Daughters typically start within roughly a year of their mother's own age. This is why our calculator treats it as the primary anchor.

Your current age. Most girls in the US and Europe get their first period between ages 10 and 15, with an average around 12 to 12.5. We use your age both to constrain the prediction window and to flag results that fall outside the typical range.

Your current stage of puberty. Tanner pubertal stages map fairly tightly to time-to-menarche. Breast budding usually precedes the first period by about 2 to 2.5 years; underarm and pubic hair, around 1 to 2 years; a growth spurt, 6 to 12 months; and clear or whitish discharge, about 6 to 12 months. We use whichever signal is strongest in your input.

The result is an educational estimate, not medical advice. Many other factors (nutrition, body weight, athletic activity, family history beyond mom, overall health) can shift your actual date by 6 to 18 months. If something feels off, talk to a pediatrician.