Date Calculator — Add, Subtract & Days Between Dates Guide

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. The TetraKits Date Calculator runs entirely in your browser — free, private, and ready on mobile or desktop.

Overview

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.

How to use the date calculator

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.

Common use cases

• Choose add/subtract or difference: Select Add/Subtract to shift a date forward or backward.
• Enter dates and amounts: Pick start and end dates, or enter how many days, weeks, months, or years to add or subtract.
• Read the result: See the resulting date with weekday, or total days between dates.
• Bookmark for quick access: Save the tool for repeat tasks without installing an app.