Change over time

Calendar heatmap

Colours calendar units by their associated values.

Chart
Trend over time
Seasonality

What it answers

Which calendar dates have unusually high or low values?

Shape: Calendar grid of coloured cells
What it shows: Weekday patterns, gaps and bursts.

Example

The question

Which days in the first quarter had unusually many orders?

Orders per day, January to March 2025 (calendar heatmap)

One square per day, darker purple to pink means more orders. Fridays and Saturdays are busier; mid-February (sale weekend) and one Monday in late March stand out.

Illustrative data. It belongs to no company.

When to use it

Use it when

Daily activity, attendance or operational patterns.

Avoid it when

When exact values or month-to-month totals are the main task.

How to read it

Locate dates by weekday/week layout and compare cell colours with the legend.

Note

Aggregate to one value per displayed calendar unit.

The data you need

Layout: Long table
Fields: Date: date; Value: number
One row is: One day and its aggregated value. What is the grain?
Rules: Use real calendar dates and one aggregate per day. Preserve missing dates separately from zero.
Optional: Optional Series. Use regular spacing for methods requiring it.
Preparation: Aggregate to one value per calendar day/unit and build the calendar layout; keep missing dates distinct fromzero.
Units: Time uses a stated date/time unit and sampling period; the value axis uses the measure's unit. Rates need their own explicit denominator.

A long table: one row per observation, few columns. New data adds rows.

Worked example

Data Jan 1=30, Jan 2=34, Jan 3=38. Colour those dates. Jan 3 has the highest value; unobserved days remain missing.

Date	Value
2026-01-01	30
2026-01-02	34
2026-01-03	38

All charts in the library