A number of tools and reports in Fathom calculate and show a variance between two values. This could be comparing a KPI result against it's target or budget or simply comparing the value for an account against the corresponding value in a prior period.

An example of variance values can be found in the KPI Numbers analysis tool:

#### Variance Calculation Method

Each KPI or Account in Fathom has an associated 'Unit of Measure'. The unit of measure impacts our variance calculation.

For an account the unit of measure is always 'Currency' meaning the values will display with the currency symbol based on the company settings.

A KPI can have a unit of measure that ranges from percentage, currency, times, days, ratio or even a custom value.**Variance for currency (and other units of measure)**The variance for currency amounts is calculated as:

*variance = (current value - prior value) / prior value*

The result is presented as a percentage change. There are a few caveats though where we switch to using the 'difference' method described below for percentages.

- If the prior value is zero.
- If the two values do not have the same sign.

**Variance for percentages and other units of measure (times, days, :1, custom)**

If the unit of measure is not currency then variance is calculated as the difference between the two values.

*variance = current value - prior value*

eg. If January has 10% and February has 25% the variance will be calculated as 15%.

ie. we don't calculate a percentage variance between percentage values.