Tue 29 Sep 2026 plus 30 days is Thursday, 29 October 2026.
Day numbers count from 1 January 1970 in the proleptic Gregorian calendar.
Thursday, 29 October 2026, 30 calendar days later.
Days and weeks are added to the start date's day number, a running count of days since 1 January 1970, so month lengths and leap years take care of themselves. Months and years move the month and keep the day of the month; when that day doesn't exist in the target month, the result is the month's last day, the same rule as Excel's EDATE. Business days are counted one at a time from the day after the start, stepping over the chosen weekend days.
Typical uses are due dates, return and cooling-off windows, visa and licence expiry dates and medication courses. 100 days after 15 January 2026 is Saturday, 25 April 2026, and 5 business days after Friday, 16 January 2026 is the following Friday.
Month steps can't always be undone: 31 March 2026 minus one month is 28 February, and 28 February plus one month is 28 March. Public holidays are not skipped here; the working-day deadline calculator takes a holiday list.
검증 출처: Python dateutil: date(2024,1,31) + relativedelta(months=1) = 2024-02-29 (Excel EDATE agrees)
검증 출처: Python 3.8: date(2026,1,15) + timedelta(days=100)
검증 출처: Python dateutil: date(2024,2,29) + relativedelta(years=1) = 2025-02-28
검증 출처: Python dateutil: date(2026,3,31) − relativedelta(months=1) = 2026-02-28
Enter today as the start date, choose Add, type 90 and pick Days. Counting starts on the day after the start date, so 90 days from 1 January 2026 is 1 April 2026: January, February and March hold 31 + 28 + 31 = 90 days. In a leap year the same count from 1 January ends on 31 March, because February has 29 days.
28 February, or 29 February in a leap year such as 2024. A day of the month that doesn't exist in the target month is moved back to that month's last day, which is how Excel's EDATE and Python's dateutil relativedelta behave. The same rule makes 31 March minus one month 28 February 2026, and 31 August plus one month 30 September.
Count forward from the day after the start date and skip each weekend day. Friday, 16 January 2026 plus 5 business days is Friday, 23 January, 7 calendar days later; 10 business days before 15 January 2026 is 1 January. Public holidays are not skipped in this calculator, whereas Excel's WORKDAY(start, days, holidays) skips any holidays you list.
Only when the year ahead has no 29 February in it. From 15 January 2027 one year later is 15 January 2028, 365 days on, but from 1 March 2027 one year later is 1 March 2028, 366 days on, because 29 February 2028 falls in between. 29 February 2024 plus one year becomes 28 February 2025 under the month-end rule.
정확도는 입력값과 계산 방법의 가정에 따라 달라집니다. 십진 연산은 유효숫자 50자리를 사용하지만, 추정값·수치해석 방법·원본 데이터의 정밀도는 더 낮을 수 있습니다. 표시값을 반올림해도 이러한 한계는 사라지지 않습니다. 독립적인 출처의 풀이와 대조한 계산 예시: 7. 예를 들어 “31 January plus one month in a leap year”은 Python dateutil: date(2024,1,31) + relativedelta(months=1) = 2024-02-29 (Excel EDATE agrees)와 대조해 확인합니다.
Howard Hinnant — chrono-compatible low-level date algorithms; Microsoft Excel EDATE and WORKDAY functions (same month-end and business-day conventions).
이 계산기에는 독립적인 출처에서 답을 얻은 계산 예제가 7개 있습니다. 테스트 모음에서 실행되며 여기에서도 실행할 수 있습니다.
두 날짜 사이의 간격을 일수, 연·월·일, 주와 시간으로 계산하고, 주말과 직접 지정한 휴일을 제외한 영업일도 계산합니다.
The deadline N business days after or before a start date, skipping weekends and the holidays you list, with the calendar days it spans.
모든 시간대에서 지정한 날짜와 시각까지 남거나 지난 일·시·분·초를 실시간으로 표시하고 시각 변경을 반영합니다.
생년월일에서 원하는 날짜의 정확한 나이를 연·월·일로 계산하고, 다음 생일과 월·주·일·시간 단위의 나이도 표시합니다.