Month addition preserves the day number where possible. Adding 1 month to January 31 gives February 28 or 29 in a leap year. Holiday exclusions must be applied manually.
Contract and legal deadlines using "days" language are rarely self-defining. Under the Federal Rules of Civil Procedure Rule 6, "days" means calendar days unless the rule specifies "business days," and when the last day falls on a weekend or court holiday, the deadline automatically rolls to the next business day. State rules differ, with many civil codes applying their own day-counting conventions. In commercial contracts, "30 days from delivery" typically anchors to the date goods are received, which differs from "30 days from invoice date" in ways that can move the deadline by a week or more.
The practical difference between calendar and business days matters most when deadlines land near month-end or holiday clusters. A 30-day window starting December 15 ends January 14, crossing the year boundary and spanning multiple holidays that may not be excluded depending on jurisdiction. For payroll contexts, converting partial hours into decimals using a time-to-decimal calculator helps when computing compensation owed within a deadline window. For age-based legal deadlines, such as those tied to a minor reaching majority, a chronological age calculator determines the exact trigger date from a birth date. When a deadline also creates overtime obligations for work completed inside it, a time and a half calculator handles the compensation side of that same date range.
| Period | Cal days | Biz days |
|---|---|---|
| 1 week | 7 | 5 |
| 2 weeks | 14 | 10 |
| 30 days | 30 | ~22 |
| 45 days | 45 | ~32 |
| 60 days | 60 | ~43 |
| 90 days | 90 | ~65 |
| 6 months | ~182 | ~130 |
| 1 year | 365 | ~261 |
To find when to start a task: enter the deadline as the start date and use Subtract mode. The result tells you the latest start date to meet the deadline.