Date Calculator

The date calculator answers questions like "what is 30 days from June 15, 2026?" or "what date was 90 business days ago?". Set a base date, choose add or subtract, pick an amount and unit, and you instantly get the resulting calendar date, its day of the week, and how many actual days separate it from the base.

How it's calculated

Days          : result = base ± N days
Weeks         : result = base ± (N × 7) days
Months/Years  : calendar shift; day clamped to the
                end of the target month if needed
Business days : step one calendar day at a time,
                skipping Saturdays and Sundays

Business-days mode. With "skip weekends" on, each step lands only on Monday–Friday, which is how contract deadlines, shipping estimates, and payroll cutoffs are usually counted. Five business days from a Monday is the following Monday (7 calendar days). This mode applies to days and weeks only — months and years always shift the calendar directly — and it does not skip US federal holidays, so a deadline that crosses Thanksgiving or July 4 may land one business day earlier than your counterparty expects.

Month-end clamping. Adding 1 month to January 31 can't land on "February 31", so the calculator clamps to the last real day of the target month: February 28 (or February 29 in a leap year). The same rule applies when adding years to February 29.

Leap years and DST. All arithmetic uses real calendar dates, so leap years are handled exactly, and the "days from base" figure is rounded so daylight-saving transitions never skew it by an hour.

Assumptions and limitations. If the base day exceeds the month's length (e.g., day 31 in June), it is clamped to the month's last day before calculating. Business-day stepping is capped at 7,000 iterations, which comfortably covers the 1,000-week maximum. For the gap between two specific dates, use the date difference calculator instead.