Day Calculator, Add Days
Add or subtract any number of days from any date, instantly
Whether you're working out a deadline, a delivery window, a lease term, or just how many days until something important, this calculator adds or subtracts days from any starting date and hands you the exact result, in calendar days or business days, with weekends and your own custom dates excluded if you need that.
Enter a date and a number of days to see the timeline
Step 1 · Set up the calculation
Enter your starting date and day count
Pick a date, choose whether you're adding or subtracting, and tell it how many days. Every field below explains exactly what it changes.
The date you're counting from. This doesn't have to be today, it can be any past or future date.
How many days to add or subtract from your starting date.
Calendar days count every day. Business days skip weekends, and optionally your own holiday dates, so the count only includes working days.
Step 2 · Your result
See the difference
Calendar days versus business days, side by side
The gap between these two counting methods grows fast. Here's what your chosen number of days looks like under three common conventions, all starting from the same date.
| Method | Resulting date | Day of week |
|---|---|---|
| Calendar days, every day counted | - | - |
| Business days, weekends skipped | - | - |
| Business days, weekends and your holidays skipped | - | - |
How this works
The logic behind every calculated date
This tool uses direct calendar arithmetic under the Gregorian calendar, the civil calendar standard referenced by ISO 8601 for representing and exchanging dates. There's no rounding, no approximation, and no hidden assumptions about month length, since every month and leap year is handled exactly as the calendar defines it.
Adding or subtracting calendar days
The calculator moves forward or backward one day at a time from your starting date until it reaches your chosen count, correctly rolling over month boundaries, year boundaries, and leap years like February 29th along the way.
Business day counting
When business days are selected, each day is checked against your chosen weekend definition and, if enabled, your custom holiday list. Days that match either are skipped and don't count toward your total, so the result reflects only working days.
For example, adding 10 business days to a Monday under a Saturday and Sunday weekend typically lands two calendar weeks later, on the following Monday, because two weekends fall inside that span. Add a couple of public holidays into the mix and that same 10 business day count can push the result out even further, which is exactly the kind of shift this calculator accounts for automatically.
Common questions
Frequently asked questions
How do I add a certain number of days to a date?
Enter your starting date, choose add days, type in how many days you want to add, and the calculator returns the exact resulting date along with its day of the week.
What's the difference between calendar days and business days?
Calendar days count every single day including weekends and holidays. Business days only count working days, which typically means skipping Saturday and Sunday, and optionally any public holidays you specify.
Can I subtract days from a date instead of adding them?
Yes, switch the operation toggle to subtract days and the calculator will count backward from your starting date instead, which is useful for working out when something needed to begin to be finished by a certain deadline.
Does this calculator handle leap years correctly?
Yes, all date arithmetic follows the Gregorian calendar exactly, so leap years and their extra day in February are automatically accounted for whenever a calculation crosses one.
How do I exclude weekends when counting business days?
Switch the day counting method to business days, then pick the weekend definition that matches your country, since some regions treat Friday and Saturday as the weekend rather than Saturday and Sunday.
Can I skip specific holiday dates in the calculation?
Yes, once business days are selected you can turn on the holiday option and list your own dates. Each one is excluded from the count along with regular weekends.