Age is calculated by subtracting your date of birth from a reference date. The calculator does this two ways: calendar arithmetic for years/months/days, and exact millisecond differences for total days/hours/minutes.
Chronological Age vs. Biological Age
Chronological age is the time elapsed between your date of birth and a reference date. It's what this calculator computes and what "age" means in legal, medical, and everyday contexts.
Biological age estimates how "old" your body is physiologically based on biomarkers like blood panels or DNA methylation. Two people with the same chronological age can have very different biological ages depending on health, genetics, and lifestyle.
Leap Years
Leap years are handled automatically. Total days are computed from actual elapsed milliseconds, which means leap days (Feb 29) are counted whenever they fall within your age span. Two people born on the same calendar date in different years can have slightly different total-days-alive counts because of how many leap years they each lived through.