# Add a calculation
URL: https://docs.awellhealth.com/docs/design-care-flows/add-a-calculation

> For the complete documentation index, see [llms.txt](https://docs.awellhealth.com/llms.txt).





A calculation turns data a care flow has collected into a score, and the care flow can branch on that
score or put it in a report.

## Add the calculation action [#add-the-calculation-action]

1. Double-click the step that will hold the calculation.
2. Click **Add action** and choose **Calculation**.
3. Name the calculation action.

<img alt="A calculation action, with the instrument selected and each of its inputs mapped to a data point" src="__img0" />

**Connect to form** ties the calculation to the form that feeds it, so it only runs once that form is
complete and is skipped if the form expires.

## Prefer a validated calculation from the Awell Score suite [#prefer-a-validated-calculation-from-the-awell-score-suite]

Awell supports many calculations based on **validated questionnaires**, available in the CE-marked
[Awell Score](/docs/improve-and-analyse/awell-score) library.

Standardizing on an established instrument beats writing a new questionnaire: the measurement can be
trusted, the data is higher quality, and other people interpret the results the same way.

So prefer an existing validated instrument for patient-reported outcome and experience measures, or
PROMs and PREMs, unless there's a specific reason not to.

## Input keys have to match what the instrument expects [#input-keys-have-to-match-what-the-instrument-expects]

A calculation needs its input data points to match what the instrument expects. For each calculation,
Awell Score publishes the documentation that explains how its questions, answers and scoring work, and
how results should be interpreted.

For each calculation Awell provides a proposed **question and question key**, for example
`PROMIS_10_...`. Use the proposed keys. The calculation matches on them, and a renamed key means the
calculation can't find its input.

Library questionnaires already carry the keys their calculation expects, so
[importing the questionnaire](/docs/design-care-flows/import-export-form-questions) avoids renaming
altogether.

## Simulate the calculation before a patient reaches it [#simulate-the-calculation-before-a-patient-reaches-it]

Simulate the calculation and read its documentation first. A calculation given the wrong input still
returns a score rather than an error, so the mistake shows up only in the result.

## Next steps [#next-steps]

**Next:** [Use variables in your actions](/docs/design-care-flows/use-variables-in-your-actions) to put
the score into a message or a clinical note.