How I add or subtract dates without counting calendar squares

Date math is easy to get wrong because months have different lengths and weekends may or may not count.

The Date Calculator tool handles the repetitive part so I can focus on checking whether the result makes sense.

The simple idea

Date math is easy to get wrong because months have different lengths and weekends may or may not count.

I still treat the output as something to review, especially when it affects money, dates, privacy, or production data.

Step 1: Enter the start date

Enter the start date.

Step 2: Choose add, subtract, or duration mode

Choose add, subtract, or duration mode.

Step 3: Enter days, weeks, months, or years

Enter days, weeks, months, or years.

Step 4: Check the resulting date

Check the resulting date.

Step 5: Use business-day mode only when weekends should be excluded

Use business-day mode only when weekends should be excluded.

Step 6: Review month-end cases carefully

Review month-end cases carefully.

Step 7: Document the rule used when sharing the date

Document the rule used when sharing the date.

My checklist

Before I trust the result, I check:

• Enter the start date.
• Choose add, subtract, or duration mode.
• Enter days, weeks, months, or years.
• Check the resulting date.
• Use business-day mode only when weekends should be excluded.
• Review month-end cases carefully.
• Document the rule used when sharing the date.

A small tool is most useful when it makes the work visible and easy to verify.