Conversion rate change: percent vs percentage points

When this helps

You are preparing a release report. A line saying “conversion grew by 0.6%” is ambiguous: a reader might understand relative growth when you mean the difference between two rates. Keep the baseline, the new rate and the traffic beside the result.

How to calculate it

1. Enter the rates as plain numbers in percent units: 4.1 means 4.1%, not a fraction of 4.1. Keep the unit in a comment.
2. Subtract the two numbers for percentage points. For relative growth, divide the new rate by the old rate, subtract 1 and multiply by 100.
3. Divide each rate by 100 before multiplying by traffic to compare expected orders at the same volume.

Inputs and formulas

Copy these lines into Sumico or use the interactive example below. Decimal values in expressions use a dot.

# Conversion before and after
old = 4.1 // percent
new = 4.7 // percent
visits = 10000

Change in pp: new - old
Growth percent: (new / old - 1) * 100
Orders before: visits * old / 100
Orders after: visits * new / 100
Extra orders: visits * (new - old) / 100

Read the result

The difference is 0.6 percentage points. Relative growth is 14.63% when rounded to two decimals. Expected orders move from 410 to 470, an increase of 60 at the same traffic volume.

The calculation in Sumico

Change an assumption

Change new = 4.7 to new = 5, keeping the percent comment. The difference becomes 0.9 percentage points, relative growth becomes 21.95% and the same traffic produces 90 additional expected orders.

Assumptions and limits

This is arithmetic, not an A/B test significance calculation. It does not establish causation or account for sample uncertainty, traffic quality, seasonality or changes in the conversion definition. Relative growth is undefined when the baseline rate is zero.

A common question

Is an increase of 0.6 percentage points the same as 0.6% growth?

No. Percentage points subtract the two rates directly. Relative percent growth compares that difference with the starting rate. Always label which measure you report.