# Error: Incorrect Format. First Argument in Date Arithmetic Should Be a Date

This error means the first value in your date math is not a valid date.

S-Docs expects the first argument in `<MATH type="date">` to be:

* a date field
* or a static date in `yyyy-MM-dd` format

If the value is missing, text-based, or actually a datetime field, the calculation fails.

### Common causes

This error usually happens when:

* the field is blank
* the field is not a date field
* the field is a datetime field, not a date field
* the math expression starts with plain text instead of a date value

### Example of the problem

This will fail because `SERVICE INSTRUCTIONS` is not a date:

{% code title="invalid-date-math.txt" %}

```
SERVICE INSTRUCTIONS + DAYS(21)
```

{% endcode %}

This can also fail if the merge field looks like a date to a user, but actually stores both date and time.

### Correct pattern

Start the math expression with a real date field.

{% code title="valid-date-math.xml" %}

```xml
<MATH type="date">{{!Opportunity.CloseDate}} + DAYS(21)</MATH>
```

{% endcode %}

You can also format the result on the `<MATH>` tag.

{% code title="formatted-date-math.xml" %}

```xml
<MATH type="date" format-date="M/dd/yyyy">
  {{!Opportunity.CloseDate}} + DAYS(21)
</MATH>
```

{% endcode %}

### How to fix it

Check each date math block in your template source.

Then confirm these items:

* the first value is a real date field
* the field is not blank
* the field is not a datetime field
* the tag includes `type="date"`

If you are using a static date, use this format:

`2026-03-24`

### Quick checklist

Before you test again, confirm:

* your tag starts with `<MATH type="date">`
* the first argument is a date
* static dates use `yyyy-MM-dd`
* you are not using descriptive text in place of a date field

{% hint style="info" %}
If a field includes both date and time, it may still fail in date arithmetic. Use a true date field whenever possible.
{% endhint %}

### Next step

For a beginner walkthrough, see [Get Started with Calculations](broken://spaces/WKNnJmhJBQwhdk5WBFsi/pages/AWClXpysUyYPXaqZa7po).


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