Date Calculator
Add or subtract days, calculate duration, with business day logic.
The Math Behind It
Date addition or subtraction calculates a new date by adding or subtracting a specified number of calendar or business days from a given start date.
Manual Calculation Example
Let's add 10 calendar days to March 1, 2026.
Frequently Asked Questions
How many business days are in a week?
Does this calculator account for leap years?
Can I calculate 90 days from today?
Mastering the Calendar
Time is linear, but calendars are messy. With months ranging from 28 to 31 days and leap years adding an extra day every four years, calculating "90 days from now" isn't as simple as adding 3 months.
This tool handles the heavy lifting of Gregorian calendar math, letting you plan deadlines, calculate project durations, and track milestones with precision—whether you count weekends or not.
Business vs. Calendar Days
Calendar Days count every single day—good for shipping estimates or biological timelines (like pregnancy).
Business Days skip Saturdays and Sundays. This is standard for corporate deadlines, bank transfers, and legal notices.
The Leap Year Rule
A year is actually 365.2425 days long. To keep our calendar aligned with the Earth's orbit, we add a day every 4 years.
Exception: Years divisible by 100 aren't leap years, unless they are also divisible by 400!
Example Scenarios
Did you know?
The Gregorian calendar skips leap years on century years unless they are divisible by 400. So 1900 was not a leap year, but 2000 was.