How to Calculate Age in C++ (chrono and Birthday Logic Examples)

Age in C++ is usually the number of completed years. The basic pattern is simple: subtract years, then reduce by one if the birthday has not happened yet this year.

Fast option: use an online age calculator

If you want to verify the answer, or you need an exact result in years, months, and days, use a calculator first and then mirror the logic in code.

Open the age calculator and enter the date of birth plus the reference date.

Simple C++ example

This example uses a plain birthday check. It is enough for many apps and coding tasks.

struct Date {
    int year;
    int month;
    int day;
};

int ageYears(const Date& dob, const Date& asOf) {
    int years = asOf.year - dob.year;
    if (asOf.month < dob.month || (asOf.month == dob.month && asOf.day < dob.day)) {
        years--;
    }
    return years;
}

Using chrono for the current date

You can get today from std::chrono and then pass the parts into the same age function.

#include <chrono>

auto today = std::chrono::floor<std::chrono::days>(std::chrono::system_clock::now());
// Extract year, month, day and compare with dob

FAQ

Is there a built-in age function in C++?

No. Usually you store the birth date, compare it with the reference date, and adjust if the birthday has not happened yet.

What about leap-year birthdays?

For February 29 birthdays, decide whether your app treats February 28 or March 1 as the birthday in non-leap years, then test that rule.