# Comparative calculations

> Calculations that compare a metric against a total or a past period: percent of total and period over period.

Comparative calculations put a metric in context, either against a total (its share of the whole) or against a past period (how it changed).

## Percent of total

Calculates the percentage of a metric relative to the original value of that metric.

### Inputs

| Input | Required? | Description |
| --- | --- | --- |
| Value | Yes | The metric to turn into a share. |
| Total Value | Yes | Which total to divide by:**Grand total**: share of the overall total.**Row total** / **Column total**: share within that row or column (most useful in a pivot).**Custom**: calculate the total across the dimensions you select (for example, across Category → % within each Country). |

### Use cases

- Revenue share by product category
- Gender mix within each signup year
- Region's share of orders within a channel
- Product share of revenue within each country

## Period over period

Calculates the change of a metric between two periods.

  
  

### Inputs

| Input | Required? | Description |
| --- | --- | --- |
| Metric | Yes | The metric to compare across periods. |
| Time dimension | Yes | The date/time field to shift along.On the viz where this period over period metric is used, include this time dimension with at least hour granularity. |
| Comparison period | Yes | How far to compare:**Previous** / **Next**: a relative shift (offset + unit, such as 1 month or 1 year).**Custom**: a fixed date range to compare against. |
| Display | Yes | What to show for each row:**Period value**: the metric in the comparison period.**Change (Δ)**: absolute difference (current − comparison).**% change (%Δ)**: relative difference vs the comparison period. |

### Use cases

- This month's orders vs same month last year
- Weekly revenue vs the prior week
- Today's signups vs same weekday last week
- Campaign week GMV vs a fixed baseline week