You enter a date of birth and a target date (defaulting to today). The tool subtracts the birth date from the target using calendar components — years, months, and days — with borrowing for shorter months and leap years. Total days are computed by dividing the millisecond difference by 86,400,000. The next-birthday countdown always references the current real-world date.
Most people want to know their current age. Setting the target to today gives an instant answer. You can change it to any past or future date to compute your age at that point.
If you were born on Feb 29, the calculator counts your age correctly in non-leap years by treating March 1 as the boundary. The total-days figure is always exact regardless of leap years.
Civil age counts whole calendar years since birth and is what most legal systems use. Chronological age in total days is slightly different because calendar years vary in length (365 vs 366 days).
Yes — any valid date pair works. Keep in mind that very old dates may not account for calendar reforms (e.g., the Gregorian switch in 1582), so results before that era are approximate.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.