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Percent or Percentage Points? Show the Difference
Editorial responsibility: SearchCub
Use percentage points for the difference between two percentages, and relative percentage change for how large that difference is compared with the starting percentage. Name the counts and denominator before choosing either description.
The Office for National Statistics percentage guidance makes this distinction. Its writing conventions belong to the ONS style guide; the arithmetic below uses our own invented data, not ONS statistics.
Start With the Count and Its Denominator
In a share calculation, the numerator is the selected count and the denominator is the total it belongs to. Divide the selected count by that total and multiply by 100 to express the share as a percentage.
Consider a fictional resource catalogue in three supplied snapshots. All counts are original invented teaching data, measured in numbers of files. A checklist is one selected file; the total includes all files in that snapshot.
Snapshot | Checklists, count | All files, count | Checklist share |
|---|---|---|---|
A | 4 | 20 | 20% |
B | 6 | 20 | 30% |
C | 6 | 40 | 15% |
The calculations are:
A: 4 / 20 × 100 = 20%.
B: 6 / 20 × 100 = 30%.
C: 6 / 40 × 100 = 15%.
These labels identify separate supplied snapshots. They do not describe a measured website or establish why its file list changed.
Say What Changed From A to B
The checklist share moves from 20% to 30%. Its difference is 30 - 20 = 10 percentage points. Subtract the percentages directly when you want that difference.
Relative percentage change uses the starting share as its baseline:
(30 - 20) / 20 × 100 = 50%.
Both statements below describe the same supplied change accurately:
In the invented catalogue, the checklist share rose from 20% to 30%, an increase of 10 percentage points.
In the invented catalogue, the checklist share rose by 50% relative to its starting share of 20%.
The first gives the difference between the shares. The second says that difference is half of the starting share. Saying only “the share increased by 10%” would give a different meaning from a rise of 10 percentage points.
The selected count also rose by 2 files, from 4 to 6. That is a count statement with its own unit. Here its relative increase is also 50%, because A and B use the same total; do not assume that agreement when the denominator changes.
Check the Denominator When Comparing A With C
Snapshot C contains 6 checklists out of 40 files. Compared with A, there are 2 more checklists, but they make up a smaller share of the catalogue.
The share difference is 15 - 20 = -5 percentage points: a fall of 5 percentage points. Its relative change is (15 - 20) / 20 × 100 = -25%, a fall of 25% relative to A's share.
An accurate completed sentence is:
The invented catalogue has 6 checklists instead of 4, while their share falls from 20% to 15% because the supplied total changes from 20 to 40 files.
That explains the arithmetic relationship within the supplied inputs. It does not identify the real-world reason for adding files or imply that the catalogue became better or worse. Decide whether your reader needs a count, a share or both, and keep the underlying values visible.
Handle Zero and Missing Baselines Explicitly
A separate teaching change from 0% to 10% has a difference of 10 percentage points. Relative percentage change under the formula above is undefined, because it would divide by the starting value of zero. Describe the supplied start and end values instead of reporting an infinite percentage increase.
A missing starting share is a different problem: the comparison is unknown until that value is supplied. If the total itself is zero, the share formula cannot supply a percentage either. Preserve the actual count and total rather than inserting a percentage that was not calculated.
Reuse a Claim With Its Supporting Values
Download the original teaching counts (CSV) and the filled percentage claim card (Markdown). The CSV preserves all three snapshots, counts, units and the invented-data marker. The card contains the completed formulas and sentences, then reusable fields for a real claim.
Fill the selected count, total, scope and comparison baseline before writing the sentence. Calculate the share from the complete values, choose the difference your sentence names, and compare the final wording with that calculation. Keep unknown inputs unknown and retain any source-specific rounding or limitations when working with real data.
Use the blogger's keyword guide to choose the reader's question, the writing guide to build its answer, and an article brief to record which number that answer needs.