Getting date math right

Day differences use calendar dates, so daylight saving changes never throw them off. Age is shown in years, months, and days, with a countdown to the next birthday and the weekday you were born. When adding months, a day that does not exist in the target month is clamped to its last day, so January 31 + 1 month is February 28 or 29. Working days count Monday to Friday only, without public holidays.