let

The let() function will allow you to assign a value to a variable, and then use that variable in the expression.

let(variable, value, expression)
Code language: JavaScript (javascript)

Note that the resulting variable can only be used between the parentheses of the original let() function, not outside of them.

let(), along with its big brother lets, is one of the most useful functions in Notion’s formula language. Here are a few of its primary uses:

• Define a variable with complex logic, then reference it in multiple places throughout a formula
• Separate formula logic from display (e.g. using variables when constructing final string values)
• Access the current variable of an outer List function within an inner List function (e.g. map(filter())

Example Formulas

/* A simple example */

let(
  lastItem,
  ["Luffy", "Zoro", "Nami", "Usopp"].last(),
  lastItem + " is the most recent addition to the crew."
)

/* Output: Usopp is the most recent addition to the crew. */

/* let() is also good for accurately setting plurality */
let(
  plurality,
  if(
    prop("Owned Books") == 1,
    "",
    "s"
  ),
  "I own " + prop("Owned Books") + " book" + plurality
)

/* Sample Outputs: "I own 1 book", "I own 24 books" */

/* Complex logic (a birthday calculation) is saved in a variable */
let(
  birthdayThisYear,
  (now().year() + "-" + prop("Birthday").formatDate("MM-DD")).parseDate(),
  birthdayThisYear.dateAdd(
    if( today() > birthdayThisYear, 1, 0 ),
    "years"
  )
)

/* Output (assume Birthday prop value is December 14, 1994 and today is March 20, 2025): Dec 14, 2025 */
Code language: JavaScript (javascript)

A variable defined in an outer instance of let() can be used within an inner instance of let(). However, if the inner instance has a variable of the same name, the outer one will be overridden in that inner context.

let(
  firstName, "Monkey",
  let(
    lastName, "Luffy",
    firstName + " D. " + lastName
  )
)

/* Output: Monkey D. Luffy */

/* An inner variable will override an outer variable of the same name. */

let(
  lastName, "Luffy",
  "Monkey D. " + let(
    lastName, "Garp",
    lastName
  )
)

/* Output: Monkey D. Garp */
Code language: JavaScript (javascript)

You can see more detailed examples, along with an example database, in the article for lets():

lets – Thomas Frank

thomasjfrank.com