Formula custom fields allow you to create relationships between custom fields using simple or advanced formulas.

For example, if you have two existing custom fields ('Cost per person' and 'Number of people') you could create a formula custom field ('Total cost') to multiply their values.

Formula custom fields are available for both project and action custom fields. To create a new formula, create a new custom field and choose the field type 'Formula'.

Please see here for a full list of supported formulas.

## Mathematical Functions

### Custom field syntax

Formula custom fields take the following structure:

field("[custom field 1]") (operator) field("[custom field 2]")

In the example above, you would define 'Total cost' by writing the following phrase in the formula field:

field("Number of people") * field("Cost per person") You could change the formula by switching out the operator (*, -, +) or by switching the custom fields.

## Date and Time Functions

Below is a table of basic date and time functions.

 Syntax Example Expected Output DAY(date) DAY('2/14/22') 14 MONTH(date) MONTH('2/14/22') 2 YEAR(date) YEAR('2/14/22') 2022 NOW() NOW() Current date/time

You can also reference 'Date' custom fields when creating new formulas.

For example, you had a custom field type = date (Kickoff Date) you could create a field which calculated the time elapsed since kickoff. The formula would be:

DAYS(NOW(),field("Kickoff Date")) 