TetraKitsDate Calculator
Add or subtract days, weeks, months, and years from any start date — or find the exact number of days between two dates. Results include weekday names for deadlines, project timelines, and contract terms.
Read: Date Calculator Guide: Add Days & Find Date Differences →
- Free to Use
- No Signup
- Privacy Friendly
How to calculate dates
- 1
Choose add/subtract or difference
Select Add/Subtract to shift a date forward or backward. Select Days Between to count days from date A to date B.
- 2
Enter dates and amounts
Pick start and end dates, or enter how many days, weeks, months, or years to add or subtract.
- 3
Read the result
See the resulting date with weekday, or total days between dates. For age from birth, use the age calculator.
Date math explained
Add / Subtract: A start date plus N days moves forward on the calendar; negative N moves backward. The calculator accounts for month lengths and leap years.
Difference: The span between two dates is the count of full days from the earlier date to the later date (exclusive or inclusive depending on context — this tool reports the absolute day count).
Example: Jan 15 + 45 days = Mar 1 (in a non-leap year starting mid-January).
Why Use This Tool?
Two Modes
Add/subtract days or measure the gap between two dates.
Leap-Year Safe
February 29 and varying month lengths handled correctly.
Date Pickers
Native inputs for fast selection on any device.
Local
Dates are processed in your browser only.
Frequently Asked Questions
How are months added to a date?
Adding months adjusts the calendar month, clamping to the last valid day when needed — Jan 31 + 1 month becomes Feb 28 (or 29 in leap years).
Does the calculator count leap years?
Yes. Day differences and date arithmetic account for leap days in February.
Can I find days between two past dates?
Yes. Enter any two dates and the tool returns the exact day count and weekday for each.
Is the start date included in day counts?
Days between counts the span from start to end. Check your use case — some contracts count inclusively, others exclusively.
Is this date calculator free?
Yes. Unlimited calculations with no signup; dates stay in your browser.
Deadline Math Without a Calendar
Project due dates, warranty expirations, and 90-day notice periods require reliable date arithmetic — including month-end edge cases. Add, subtract, or count days between dates with weekday labels in one step.
