Notion Formula Returns ‘Cannot Convert’ Error: Fix

You are working on a Notion database formula and see the error message “Cannot Convert” instead of the expected result. This error occurs when a formula tries to change a value from one data type to another in a way that Notion does not support. This article explains the three main causes of this error and provides step-by-step fixes to resolve each one. After reading, you will be able to identify the exact property type mismatch and correct your formula syntax.

Why Notion Shows the “Cannot Convert” Error in a Formula

Notion formulas work with strict data types. Every property in a database has a type: text, number, date, checkbox, select, multi-select, relation, rollup, formula, file, image, phone, email, URL, or person. When a formula tries to combine or convert values that belong to incompatible types, Notion displays the “Cannot Convert” error. The error message sometimes includes additional context, such as “Cannot convert ‘text’ to ‘number’,” which narrows down the problem.

The root cause is always a mismatch between the formula function’s expected input type and the actual type of the value passed. For example, the dateAdd() function expects a date as the first argument. If you pass a text string, Notion cannot convert it and throws the error. Similarly, mathematical operators like + and - expect numbers; using them on text values fails. Understanding this type system is the first step to fixing the error.

Three Common Scenarios That Trigger the Error

The error appears in three specific situations:

• Direct type mismatch: The formula’s output type does not match the type of the value it produces. For instance, a formula property set to “Number” that returns a text string.
• Incompatible property reference: The formula uses prop() to reference a property whose type cannot be converted to the required type. Referencing a “Files & Media” property inside a math operation causes the error.
• Incorrect function argument: A function receives an argument of the wrong type. replace() expects three text arguments; passing a number as the second argument fails.

Once you identify which scenario matches your formula, you can apply the corresponding fix.

Steps to Fix the “Cannot Convert” Error in Notion Formulas

Fix 1: Correct the Formula Output Type

1. Open the database and locate the formula property
   Go to your Notion database. Click the property header of the formula column that shows the error. Select Edit property from the menu.
2. Check the formula property type setting
   In the property editor, look for the Type dropdown. It shows the expected output type for the formula. Options include Number, Text, Date, Checkbox, and others. Ensure this type matches what your formula actually returns.
3. Change the type to match the formula output
   If your formula produces a date but the type is set to Number, change the type to Date. Or, if the formula returns a text string but the type is set to Number, change it to Text. After changing, the error should disappear.
4. Use explicit conversion functions if needed
   If you cannot change the output type because other formulas depend on it, wrap the result in a conversion function. To convert a number to text, use format(prop("Number Property")). To convert text to a number, use toNumber(prop("Text Property")).

Fix 2: Remove or Replace Incompatible Property References

1. Identify which property reference causes the error
   Look at each prop("Property Name") in your formula. Note the type of each referenced property. Hover over the property name in the formula editor to see its type.
2. Replace unsupported property types
   Properties of type File, Image, Phone, Email, URL, Person, Relation, or Rollup cannot be directly used in most formulas. If you need the value, extract a compatible subvalue. For a Person property, use prop("Person").first().name to get the name as text. For a Relation, use prop("Relation").first().prop("Name") to get a linked page’s title.
3. Remove the incompatible reference if not needed
   If the formula does not actually need that property, delete the prop() reference. For example, if you accidentally included prop("Image") in a math formula, remove it.

Fix 3: Correct Function Argument Types

1. Check each function’s argument requirements
   Refer to Notion’s formula documentation for each function you use. For example, dateAdd(date, number, string) requires a date, a number, and a unit string like “days”. replace(text, text, text) requires three text values.
2. Wrap arguments in type converters
   If an argument is the wrong type, use format() to convert a number to text, or toNumber() to convert text to a number. For date conversions, use fromTimestamp() or parseDate() when needed.
3. Test each function separately
   Simplify your formula to a single function call. Test it with static values — for example, dateAdd(now(), 3, "days"). If it works, gradually add back other parts until you find the exact argument causing the error.

If Notion Still Shows “Cannot Convert” After the Main Fix

Formula references a rollup with an incompatible aggregation

Rollup properties can aggregate values from related databases. If the rollup’s aggregation method produces a type that your formula cannot handle, the error persists. For example, a rollup set to “Show original” returns an array, not a single value. Wrap the rollup reference in first() or join() to get a single value of the correct type.

Formula uses a select or multi-select property without extracting the name

Select and multi-select properties return objects, not plain text. When you use prop("Select Property") in a text formula, Notion cannot convert the object to text. Use prop("Select Property").name to extract the option name as text. For multi-select, use prop("Multi-Select Property").first().name or join(prop("Multi-Select Property").map(current.name), ", ").

Formula contains a nested function that returns a type mismatch

Sometimes the outer function receives a value from an inner function that is not the expected type. For instance, format(dateAdd(now(), 3, "days")) works, but dateAdd(format(now()), 3, "days") fails because format() returns text, not a date. Check the return type of each nested function and ensure it matches the outer function’s input requirement.

Notion Formula Error Causes and Fixes Compared

Error Scenario	Cause	Fix
Formula type set to Number but returns text	Output type mismatch in property settings	Change property type to Text or wrap result in toNumber()
prop("Image") used in a math formula	Incompatible property type (File/Image)	Remove the reference or replace with a compatible extracted value
dateAdd(prop("Text Date"), 1, "days")	Function expects date but receives text	Use parseDate() to convert text to date first
replace(prop("Number"), "a", "b")	Function expects text but receives number	Use format(prop("Number")) to convert to text
Rollup property used directly without aggregation	Rollup returns an array (Show original)	Add first() or join() to extract a single value

The table above summarizes the three main scenarios you will encounter. Matching your error to one of these rows gives you a direct fix path.

Conclusion

You can now identify why Notion shows the “Cannot Convert” error and apply the correct fix. Check the formula property output type first, then inspect each prop() reference for incompatible types, and finally verify function argument types. Use format(), toNumber(), parseDate(), and .name to convert values between types. For complex formulas, test each function individually to isolate the problematic argument. If you work with rollups or multi-select properties, remember to extract single values before using them in calculations.