Choosing the Right Chart: Data Visualisation for Finance Reports

The best chart for a finance report is the one that lets a reader see the point quickly and accurately. This guide sets out principles for choosing and labelling charts, drawing on the UK Government Analysis Function's "Data visualisation: charts" guidance (publication date shown: 19 May 2022) and its "Accessible charts: a checklist of the basics" (2 May 2023). Please note this is UK government method guidance written for people in UK government who publish charts. It is not Irish law or an Irish standard, and it covers static charts rather than interactive dashboards. We use it because it is clear and published openly, and the principles carry across to most finance reports prepared in Dublin or anywhere else.

If your next step is building the dashboard itself, see our guide to financial dashboards in Excel for executive reports.

Start with the message

The guidance begins with the message. It suggests testing whether you can state it briefly: if you cannot write down the message your chart is giving in a few sentences, reconsider the chart. A finance example (our suggestion, not the guidance's): "Overheads have risen faster than revenue for three quarters" is a message a chart can support; "here is everything" is not.

Match the chart to the relationship

The guidance maps relationships in the data to chart types. A selection of its mapping, which is not the full list:

• Distribution: bar charts, population pyramids, box plots or dot plots.
• Time series: line charts or calendar heat maps.
• Ranking: bar charts, lollipop charts or slope charts.
• Deviation: bar charts or dot plots.
• Correlation: scatterplots or line graphs.
• Magnitude: bar charts.
• Spatial data: maps.
• Part-to-whole: bar, pie, donut, tree map or bubble charts.
• Flow: Sankey graphs.

For the chart types finance teams use most, the guidance gives specific limits:

• Bar charts suit comparing categories, ranking and deviation from a fixed value. Use a line chart instead when a bar chart would show more than one time series.
• Stacked bar charts are best for comparing several part-to-whole relationships. The guidance advises limiting each stack to four categories and avoiding them for data with negative values, suggesting small multiples instead.
• Clustered bar charts compare categories within and across groups; limit clusters to four bars and avoid them for time series.
• Line charts are mainly for time series. Keep to about four lines, and consider small multiples for more.
• Pie charts only when there are five categories or fewer, the categories sum to a meaningful whole and there is a dominant category. If several categories are a similar size, use a bar chart instead.

Axes: do not distort

The guidance is direct on axes. For bar charts, do not break the numerical axis, because it distorts relative proportions. For line charts, breaking the y-axis is acceptable when necessary, with a clear break symbol, a rounded break point and a description of the break in the text. It says dual-axis charts are generally not recommended because they are easily misinterpreted or manipulated, and suggests separate charts with their own axes. It also notes that the aspect ratio changes how steep a line looks, so choose a neutral ratio.

For time series, the guidance says to always highlight breaks, and not to join points either side of a missing value. In finance, a missing period (for example, a quarter with no data) is exactly where this matters.

Titles, labels and sources

Per the guidance, all charts need at least one title, but best practice is two: a headline title and a statistical subtitle that includes the data type, geography and time period. It advises direct labelling of categories and lines instead of a legend, because legends rely on colour matching. Other documented points:

• Text should always be horizontal; if labels do not fit, transpose the chart or change units.
• Use a sans serif font, large enough to read after resizing.
• Use commas as thousands separators, for example 121,576.
• Give the specific publication or dataset as the source, and put footnotes in body text.
• Provide an accessible data download for each chart.
• Use annotations if they help tell the story, keep them concise and close to the relevant data, and do not overuse them.

On value labels, the guidance says best practice is complicated and suggests testing; it also observes that a well-structured table can often be as powerful as a chart. For a finance audience that wants exact figures, a table may be the better choice, a point worth taking seriously.

Sorting and simplicity

The guidance says to always rank bars by value, unless there is a natural order such as age or time. For pie charts, rank the sectors by size and start the first at 12 o'clock. On formatting, it advises avoiding shaded backgrounds, unnecessary borders, patterns, 3D effects, shadows and unnecessary markers. It advises a maximum of about ten gridlines, in light grey, and says the gap between bars should be narrower than the width of a single bar.

Colour and accessibility

The guidance's colour advice in the charts page is practical: for a focus chart, give a colour to the series of interest and use light grey for the others. In general, the guidance says not to rely on colour as the only way to match labels to data. The checklist adds that you should only use colours with the required level of contrast against the background, with black or dark grey text for line labels. Detailed palettes and contrast thresholds sit in a separate colours guidance so this guide does not quote ratios.

On accessibility, the page states that UK public sector content must meet WCAG 2.2 Levels A and AA, including charts. Again, that is a UK legal context. The practical takeaways that travel well are:

• Provide a text alternative: a table, a description, or both. The guidance says descriptions should not repeat the chart title, be a literal description or outline every data point.
• Start a text description by naming the chart type, for example "a line chart showing...".
• Keep titles and sources out of images, as images of text cause problems.
• Use SVG where possible because it scales without losing quality.

Our suggestion: even where no accessibility regulation applies to a given internal report, these checks help readers with colour vision difficulties and anyone reading on a small screen.

Test before you send

The guidance recommends testing charts with users, including asking colleagues who did not work on the data. For a finance report, a quick test is to show the chart to someone outside the team for ten seconds and ask what the message is. That test is our suggestion.

Whichever tool you use, the same principles apply. Our overview of Power BI for finance teams and our comparison Power BI or Tableau for accountants cover the tool side.

Learnsignal's offices are off Baggot Street in Dublin, and we offer in-person training from there. For current details, see our CPD pages.

Frequently asked questions

Is this guidance Irish?

No. It comes from the UK Government Analysis Function and is written for UK government analysts. We use it as a published method reference, not as Irish rules.

When should I use a pie chart?

The guidance says only when there are five categories or fewer, the categories sum to a meaningful whole, and there is a dominant category. If several categories are a similar size, use a bar chart.

Should I use a dual-axis chart?

The guidance says dual-axis charts are generally not recommended because they are easily misinterpreted or manipulated, and suggests separate charts.

Do I need a legend?

The guidance advises direct labelling instead of legends where possible, because legends rely on matching colours.

Start with the message, choose the simplest chart that carries it, label it directly, and add a text alternative; those habits improve most finance reports.