Calendar-exact difference between two dates with honest borrowing math

Worked example: sibling age gap, step by step

An age difference calculator gives the exact gap between two calendar dates in years, months and days — you enter two birthdays and it handles the borrowing math. Take a real one: a child born March 14, 2019, and a sibling born November 6, 2024. The engine adds five whole years to land on March 14, 2024, then counts seven full months to October 14, because the next month boundary would land on November 14, past the second date. The leftover stretch borrows October's 31 days: 17 remaining October days plus 6 November days makes 23. Answer: 5 years, 7 months, 23 days. As raw days, 2,064 — which splits into 294 weeks and 6 days.

Watch what happens when the day-of-month doesn't exist in the next month. Compare January 31 to March 1 in a non-leap year: February has no 31st, so the tool treats January 31 plus one month as February 28, then adds one more day — one month, one day, not a made-up thirty-first of February. That's honest calendar arithmetic, and it matters for lease dates, trial periods and age brackets. Date order doesn't matter either; the older date is detected automatically, so the answer always reads forward.