Add/Subtract Days Calculator
Choose a start date, enter the number of days, and add or subtract to find the result date.
Common Day Offsets Reference
| Days to Add | Common Use |
|---|---|
| 7 days | One week (next or previous) |
| 14 days | Two weeks / biweekly cycle |
| 30 days | Approximate one month |
| 45 days | Net-45 payment terms |
| 60 days | Net-60 / two months |
| 90 days | One quarter / trial periods |
| 180 days | Six months / half-year |
| 280 days | Human pregnancy due date |
| 365 days | One year (non-leap) |
| 366 days | One year (leap year) |
Date Arithmetic in Business
Many business and legal processes are defined in terms of calendar days from a trigger date. Common examples include:
- Net payment terms — Net-30 means payment is due 30 days after the invoice date
- Statute of limitations — Legal claims must be filed within a set number of days from when the cause of action arose
- Probationary periods — Employees are often on probation for their first 90 days
- Insurance waiting periods — Coverage may not begin until a certain number of days after enrollment
- Subscription renewals — Free trials end on the Nth day after sign-up
Frequently Asked Questions
What is this calculator useful for?
Common uses include: finding a date 30, 60, or 90 days from today for contract deadlines; calculating a due date (e.g., 280 days from last menstrual period); finding a warranty expiration date; determining when a subscription or trial period ends; and working backward from a deadline to find the start date.
How does adding days handle month and year boundaries?
The calculator uses JavaScript's built-in Date arithmetic, which automatically handles month-end rollovers and year boundaries. Adding 30 days to January 25 gives February 24, adding 10 days to December 28 gives January 7 of the next year, and so on. Leap years are also handled correctly.
Can I subtract days to find a past date?
Yes. Select the 'Subtract Days' option to go backward in time. This is useful for finding when something happened (e.g., '90 days before March 15 was December 15') or for calculating look-back periods in finance and law.
What does 'days from today' mean in the result?
The result shows how many calendar days the calculated date is from today's date. A positive number means the result is in the future; a negative number means it is in the past. This helps you quickly understand where the date falls relative to now.
How do I add months or years instead of days?
This calculator adds or subtracts calendar days. To add months, convert them to days first (30 days per month is an approximation; exact month lengths vary). For adding exact months or years, use the Days Between Dates calculator to verify the result.