---
title: "Date Math in Calculation Formulas"
slug: "date-math-in-calculation-formulas"
status: "new"
updated: 2026-07-21T20:18:37Z
published: 2026-07-21T20:18:37Z
canonical: "knowledge.technolutions.net/date-math-in-calculation-formulas"
stale: true
---

> ## Documentation Index
> Fetch the complete documentation index at: https://knowledge.technolutions.net/llms.txt
> Use this file to discover all available pages before exploring further.

# Date Math in Calculation Formulas

Calculation formulas on forms can use JavaScript date methods to add time to a date or calculate the difference between two dates. These examples assume that the referenced form fields are configured as date fields and have export keys available to the calculation.

> [!TIP]
> ⭐ Get Inspired
> 
> This article was adapted from [a post by Technolutions staff](https://community.technolutions.net/get-inspired/post/date-math-in-calculation-formulas-gVidRwpizfDHZ77) in the Slate Community Forums' Get Inspired space. Have a great idea for a Get Inspired post? [Let us know](https://community.technolutions.net/get-inspired/new?post_type=gnHx7As1gZ8r6Ld)!

## Add one year to a date

Use the following pattern to add one year to a date and return the result in `yyyyMMdd` format. Replace `date_export_key` with the export key of your date field.

```Formula
(@date_export_key.getFullYear() + 1) + ('0' + (@date_export_key.getMonth() + 1)).slice(-2) + ('0' + @date_export_key.getDate()).slice(-2)
```

The formula uses:

- `getFullYear()` to return the four-digit year.
- `getMonth()` to return the month. JavaScript months are zero-indexed, so the formula adds `1`.
- `getDate()` to return the day of the month.
- `.slice(-2)` to keep month and day values two digits long.

## Calculate the difference between two dates

JavaScript stores the difference between dates in milliseconds. Divide the date difference by the appropriate number of milliseconds for the desired unit.

### Days

```Formula
Math.floor((@date1 - @date2) / 86400000)
```

### Weeks

```Formula
Math.floor((@date1 - @date2) / 604800000)
```

### Years

```Formula
Math.floor((@date1 - @date2) / 31557600000)
```

> [!WARNING]
> 📝 Note
> 
> The year example uses 365.25 days to account for leap years. Month calculations are not included because month lengths vary.

## Test the output

1. Preview the form with sample date values.
2. Confirm that the calculation updates when the source date changes.
3. Submit a test record and verify the stored value in the form response.

📖 Learn more about [JavaScript date methods](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date).