Add Days to a Date Calculator
Enter a start date and choose how many days (or weeks, months, and years) to add or subtract. The calculator returns the resulting date and the day of the week. Switch on business-days mode to skip weekends automatically. Results update instantly as you type.
How to add days to a date
To find a date a certain number of days in the future (or past), start with your reference date and count forward (or backward) one day at a time. In practice, computers do this instantly by converting each date to a day number (days since a fixed epoch), adding the offset, then converting back. This calculator supports four units at once: years, months, weeks, and days. Years and months are applied first as calendar units (accounting for varying month lengths and leap years), then weeks and days are added on top.
Calendar days vs. business days
Calendar days count every day of the week, including weekends. Business days count only Monday through Friday, skipping Saturday and Sunday. The difference matters for deadlines, shipping estimates, and legal time limits. For example, 10 calendar days starting on a Friday includes 2 weekends and only 6 working days, while 10 business days from a Friday lands on the second Monday two weeks later. Toggle the "Business days only" option to switch between the two modes. When business-days mode is on, years and months remain calendar-based (because there is no universally agreed-upon number of working months), but days and weeks are counted as working days.
Leap years and varying month lengths
Not all years have 365 days and not all months have 30 days: February has 28 days in common years and 29 in leap years, while months range from 28 to 31 days. When this calculator adds a whole number of months it moves the month value and keeps the day the same, clamping to the last day of the month if needed (for example, adding 1 month to 31 January gives 28 or 29 February). When adding years, the same logic applies, so adding 1 year to 29 February in a leap year gives 28 February in the next common year. Adding pure days sidesteps these rules entirely because it simply advances a day counter.
Practical uses for an add-days calculator
Date arithmetic appears everywhere in daily life and professional work. Return windows and warranties are often defined as "30 days from purchase". Medication courses are prescribed as "take for 14 days". Construction and project timelines specify delivery "90 business days from contract signing". Legal statutes set appeal periods as "30 calendar days from judgment". Tax codes impose deadlines like "file within 45 days of the end of the quarter". Payroll cycles repeat every 14 or 28 calendar days. Knowing the exact result date avoids costly mistakes and last-minute scrambles.
Common date-counting reference spans
| Span name | Calendar days | Business days (approx.) | Common use |
|---|---|---|---|
| Net 30 | 30 | 22 | Invoice payment terms |
| Net 60 | 60 | 43 | Extended payment terms |
| 90 days | 90 | 65 | Trial periods, regulations |
| 6 months (approx.) | 180 | 130 | Mid-year reviews, probation |
| 1 year | 365 or 366 | 261 | Annual deadlines, warranties |
| 2 years | 730 or 731 | 522 | Statute of limitations (many jurisdictions) |
Typical time spans used in business, law, medicine, and everyday planning.
Frequently asked questions
What is 30 days from today?
Set the start date to today and add 30 days. The calculator returns the exact date and day of the week. Because month lengths vary, the answer is not simply "the same date next month" in every case.
How do I subtract days from a date?
Use the "Subtract (past date)" option in the direction selector. Enter your start date and the number of days, weeks, months, or years to subtract. The calculator counts backward and returns the earlier date.
What is the difference between calendar days and business days?
Calendar days count every day including weekends: Saturday and Sunday are included. Business days count only Monday through Friday. Toggle the "Business days only" switch to change modes. For example, 10 calendar days from a Monday is 10 days later, but 10 business days is 14 calendar days later because two weekends are skipped.
Does adding months account for different month lengths?
Yes. When you add whole months, the calculator advances the month component and keeps the day the same, clamping to the last valid day if necessary. Adding 1 month to 31 January gives 28 or 29 February, not 2 or 3 March.
How are leap years handled?
The calculator follows the Gregorian calendar rules: a year is a leap year if it is divisible by 4, except century years which must also be divisible by 400. Adding a year to 29 February 2024 gives 28 February 2025 because 2025 is not a leap year.
Can I add years, months, weeks, and days at the same time?
Yes. Fill in any combination of the four fields. Years and months are applied first (in that order), then weeks and individual days are added on top. All fields default to zero so you only need to fill in the units you care about.
What is 90 days in months?
90 calendar days is about 2 months and 29 or 30 days, depending on which months are involved. It is not exactly 3 months because months have varying lengths. Use this calculator to find the precise date: add 90 days (not 3 months) if you need an exact 90-day window.