How to Create a User-Defined Function in Power Apps

November 8, 2026 · 8 min read

Founder @ Dewiride

A user-defined function is a formula with a name and parameters. You write it once in App.Formulas, then call it from any control, exactly like a built-in function: ShiftMinutes(Date(2026, 10, 24), Time(22, 0, 0), Time(6, 0, 0)) returns 540. Change the function, and every control that calls it changes with it.

The example is the Overtime Timesheet app. The hours line, the problem message and the Save button on its Log overtime screen all need the start and finish of a shift, so the app works them out in four functions instead of repeating the formulas.

What They Are

Microsoft's App object page says to think of user-defined functions as an extension to named formulas that adds parameters and supports behavior formulas. They live in the same place as named formulas: the app's Formulas property (How to Use Named Formulas in Power Apps).

The syntax:

Syntax
FunctionName(Parameter1: Type1, Parameter2: Type2): ReturnType = Formula;

Every parameter has a type, such as Date, Time, Number or Text, and so does the result. Microsoft: you must type each parameter and the output.
= separates the signature from the formula, and ; ends the definition.
Recursion isn't yet supported: a function can call other functions, but not itself.

Prerequisites

App.Formulas: How to Use Named Formulas in Power Apps.

Step 1: Check the Setting

In Studio, open Settings → Updates → New. New analysis engine and User defined functions must be On. In this app it already was:

The Updates page of Power Apps Studio settings on the New tab, with the New analysis engine and User defined functions setting switched On and outlined in red, below Modern controls and themes, also On

Microsoft announced user-defined functions as generally available in September 2025. Since version 2508.3 they've been part of the new analysis engine switch, which is enabled by default for new apps (Power Apps' User defined functions GA).

Step 2: Write a Function

Select App in the Tree view, choose Formulas in the property list, and add the function after any named formulas already there:

App → Formulas
ShiftStart(ShiftDate: Date, StartAt: Time): DateTime =
    DateTime(Year(ShiftDate), Month(ShiftDate), Day(ShiftDate), Hour(StartAt), Minute(StartAt), 0);

ShiftStart is the name you call it by.
ShiftDate: Date and StartAt: Time are its two parameters, with their types.
: DateTime after the brackets is the type it returns.
After = is the formula, which can use the parameters by name. This one puts the start time on the shift's date (How to Combine a Date and a Time in Power Apps with DateTime).

Step 3: Build Functions on Functions

A function can call another one. ShiftEnd puts the finish on the next day when it's earlier than the start (How to Calculate Hours for an Overnight Shift in Power Apps), and ShiftMinutes counts the minutes between the two:

App → Formulas
ShiftEnd(ShiftDate: Date, StartAt: Time, EndAt: Time): DateTime =
    With(
        {EndDate: If(EndAt < StartAt, DateAdd(ShiftDate, 1, TimeUnit.Days), ShiftDate)},
        DateTime(Year(EndDate), Month(EndDate), Day(EndDate), Hour(EndAt), Minute(EndAt), 0)
    );
ShiftMinutes(ShiftDate: Date, StartAt: Time, EndAt: Time): Number =
    DateDiff(ShiftStart(ShiftDate, StartAt), ShiftEnd(ShiftDate, StartAt, EndAt), TimeUnit.Minutes);

In the formula bar, after the TimeChoices named formula:

The Formulas property of App in the expanded formula bar, with the TimeChoices named formula followed by the ShiftStart, ShiftEnd and ShiftMinutes user-defined functions, each with typed parameters and a return type

Step 4: Call It

I put the call into a text control's Text for a moment, so Studio's preview strip shows the result:

Any text control → Text
ShiftMinutes(Date(2026, 10, 24), Time(22, 0, 0), Time(6, 0, 0))

22:00 on 24 October to 06:00 the next morning, the night the UK clocks went back, is 540 minutes:

The formula bar with ShiftMinutes(Date(2026, 10, 24), Time(22, 0, 0), Time(6, 0, 0)), the preview strip reading 540 with Data type number, and the text control showing 540

Step 5: Return Text

A function can return any type. The app's fourth function, ShiftProblem, takes the shift and its break and returns the first thing wrong with them as a sentence, or empty text when there's nothing wrong (How to Validate a Form Without an Edit Form in Power Apps):

The end of the Formulas property in the expanded formula bar: the ShiftProblem function with parameters ShiftDate, StartAt, EndAt and BreakMins returning Text, built from With, DateDiff, a LookUp for a clashing entry, and an If listing each problem message

How the Example Calls Them

Where	Calls	For
The hours line	`ShiftMinutes`	The minutes worked, before the break
The problem message	`ShiftProblem`	The first problem, or nothing
The Save button	`ShiftStart` and `ShiftEnd`	The start and finish it saves to SharePoint

Each call passes the controls' values, for example:

Part of lblHoursLO → Text
ShiftMinutes(dpWorkDateLO.SelectedDate, cmbStartLO.Selected.Value, cmbEndLO.Selected.Value)

Functions That Do Things

The functions above only calculate. Microsoft's page says named formulas and most user defined functions don't support behavior functions with side effects, such as Set or Notify. To write one that does, wrap the body in curly braces; if it returns nothing, its return type is Void:

From Microsoft's App object page
Spend( Amount: Number ) : Void = {
    If( Amount > Savings,
        Error( $"{Amount} is more than available savings" ),
        Set( Savings, Savings - Amount );
        Set( Spent, Spent + Amount)
    );
}

Common Mistakes

Mistake	What happens	Do this instead
A parameter or the result without a type	Microsoft requires a type for each	`Name: Type`, and `: Type` after the brackets
No `;` between definitions	The definitions don't follow Microsoft's syntax	End each with `;`
Set or Notify in an ordinary function	Microsoft: most functions don't support them	Wrap the body in `{ }` and return Void
A function that calls itself	Recursion isn't supported yet	Use a loop such as ForAll
Copying the same formula into every control	A change has to be made in every copy	Put it in a function and call it

Troubleshooting

Symptom	Likely cause	Fix
An error when a record is passed in	Microsoft: the fields of a record value must be a proper subset of the type definition and can't include extra fields	Pass only the fields the type defines
The function isn't in the Variables pane	In this app, the pane listed named formulas such as TimeChoices, but not the functions	Read them in App → Formulas

FAQ

What's the difference from a named formula?

Parameters. A named formula is one value, such as TimeChoices, the list of times people pick from. A function works out a value from what you pass it, so ShiftMinutes gives a different answer for every shift.

Can a function use the app's named formulas and data?

Yes. ShiftProblem uses the named formula MyEmail and looks up the OvertimeEntries list to find a shift that overlaps: How to Check for Overlapping Times in Power Apps.

Conclusion

Write Name(Parameter: Type, …): ReturnType = Formula; in App.Formulas, check that New analysis engine and User defined functions is on, and call the function wherever you need it. One definition, one place to change it.

Additional Resources

App object: user-defined functions: syntax, types, behavior functions and limits.
Code optimization: user defined functions: Microsoft's coding guidance.

What They Are​

Prerequisites​

Step 1: Check the Setting​

Step 2: Write a Function​

Step 3: Build Functions on Functions​

Step 4: Call It​

Step 5: Return Text​

How the Example Calls Them​

Functions That Do Things​

Common Mistakes​

Troubleshooting​

FAQ​

What's the difference from a named formula?​

Can a function use the app's named formulas and data?​

Conclusion​

Additional Resources​

Related​