Compute a deadline date from a start date and a duration. Toggle between business days (skipping weekends and holidays) and calendar days (just counting forward). The result shows the target date plus both business-day and calendar-day counts so you always know what the deadline means in both units.
How it works
Business mode walks forward one day at a time, skipping Saturdays, Sundays, and any dates in the holiday list. Adding 10 business days to a Monday lands you on the Monday two weeks later (5 weekdays per week × 2 weeks = 10). If there’s a holiday in that range, the walk continues one more day to skip it.
Calendar mode is simpler: add N days to the start date with no skipping. Adding 10 calendar days to April 1 gives April 11 regardless of what days of the week those fall on.
Both modes also report the “other” count as a cross-check. If you asked for 10 business days, the tool tells you that’s 14 calendar days. If you asked for 14 calendar days, it tells you that’s 10 business days (assuming no holidays in range). Seeing both lets you confirm the deadline matches your mental model.
Example: a 30-business-day invoice
Invoice issued on Wednesday April 15, 2026, payment terms “net 30 business days”:
- Start: 2026-04-15
- Days: 30
- Mode: business
- Deadline: 2026-05-28 (6 weeks later = 30 business days)
- Calendar days away: 43
The deadline is 6 weeks rather than 4 because 30 business days means 6 full work-weeks. If you mentally translate “30 days” as “about a month”, the business-day reading stretches to about six weeks — a common misunderstanding between US and non-US business cultures.
Example: 14 calendar days from now
“Respond within 14 days” on a legal or administrative notice usually means calendar days in practice:
- Start: 2026-04-15 (Wed)
- Days: 14
- Mode: calendar
- Deadline: 2026-04-29 (Wed)
- Business days away: 10
Calendar mode doesn’t care about weekends — the deadline is 14 days out regardless of which days those are. If the deadline date itself lands on a weekend (check yourself — the tool doesn’t bump it), you may want to start a day earlier depending on how the issuing authority interprets the rule.
Example: adding a US federal holiday
Deadline 10 business days from May 15, 2026 (Fri), with Memorial Day (May 25, 2026, Mon) as a holiday:
- Start: 2026-05-15
- Days: 10
- Mode: business
- Holidays: 2026-05-25
- Deadline: 2026-05-30 (Sat, 11 business days later because Memorial Day skipped)
Wait — that’s a Saturday, not a business day. The math is correct: start at Fri May 15, 10 business days later ignoring the 25th would be Fri May 29, but skipping the 25th shifts that to Mon June 1 (the next available business day after May 29 + 1 more business day for the skipped holiday). Let the tool do the walk; hand-counting gets error-prone with multiple holidays.
What this tool does not do
It doesn’t support negative durations — the framing is “start + N → deadline”, not “deadline − N → start”. For backward walks, use the business day calculator with negative days.
It doesn’t ship a default holiday list. Holidays vary by country, region, and year. Provide your own.
It doesn’t model half-day holidays, floating holidays (observed on different dates in different years), or legal-calendar quirks (Saturday holidays bumped to Friday, Sunday holidays bumped to Monday). Those are domain-specific rules that this tool deliberately doesn’t assume — a wrong assumption about the rule is worse than a straightforward walk.
It doesn’t compute elapsed time in hours or minutes — this is a day-granularity tool. For sub-day durations, use the date difference calculator or the time unit converter.