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A date calculator adds or subtracts days, weeks, months, or years from a date to find a resulting date. Useful for project deadlines, contract expiration dates, subscription renewals, legal deadlines, and age milestones.

ステップバイステップガイド

1. 1Adding days: count forward from the start date
2. 2Adding months: add to the month number, handle year rollovers and month-end edge cases
3. 3Leap years: divisible by 4 (except centuries unless divisible by 400)
4. 4Business day calculations exclude weekends (and optionally holidays)

解いた例