Free Online Calendar Heatmap Maker
Show activity patterns across days and weeks. Like GitHub contribution graphs.
Create Your Calendar Heatmap Now — It's FreeWhat Is a Calendar Heatmap?
Made famous by GitHub's contribution graph, calendar heatmaps are now widely used for any daily time-series data. Key components include the day cells, a seven-row layout for weekdays, week columns spanning the year, month labels, and a color-intensity legend. They can display a full year of data in a compact strip, making long-term trends and outlier days easy to spot at a glance.
What Data You Need for a Calendar Heatmap
A flat list of dated rows, each with a date (YYYY-MM-DD) and one numeric value for that day; one row per calendar day. The tool parses the dates, places each value in a grid by week (columns labeled W1, W2, …) and weekday (rows Mon–Sun), and leaves any day you don't supply blank. Example: `2026-01-01, 12 | 2026-01-02, 0 | 2026-01-03, 47`.
When to Use a Calendar Heatmap
Calendar heatmaps work best with one value per day over at least 3 months. Choose a calendar heatmap over a line chart when the day-of-week pattern is important. Choose a standard heatmap when your axes are not time-based. The familiar calendar layout requires no explanation, making it ideal for dashboards and status pages.
Where a Calendar Heatmap Works Best
- Showing a GitHub-style contribution streak of daily commits or pull requests across a full year.
- Tracking gym attendance or a habit (meditation, reading) to spot streaks and missed days at a glance.
- Visualizing daily website signups or orders over 12 months to reveal weekday-vs-weekend and seasonal patterns.
- Plotting support-ticket volume per day to find spikes and recurring busy weekdays.
Calendar Heatmap Example: A Year of Commits
A developer logs daily git commits for 2026 to see how consistent they are. Each day is a cell shaded from pale (0 commits) to dark (10+).
Sample data: 2026-01-05, 8 | 2026-01-06, 11 | 2026-01-10, 0 | 2026-01-11, 0 | 2026-02-14, 3 | 2026-02-17, 9 | 2026-03-02, 14
Dark cells cluster on weekdays while Saturdays and Sundays stay pale, confirming a steady Mon-Fri rhythm with weekends off and a mid-week peak.
How to Create a Calendar Heatmap Online
- Step 1: Open ChartLoad and select the Calendar Heatmap type from the chart picker on the main page
- Step 2: Enter dates in the first column (YYYY-MM-DD) and corresponding values in the second column
- Step 3: ChartLoad auto-arranges your data into a calendar grid with weeks as columns and weekdays as rows
- Step 4: Choose a color scale such as green (GitHub style), blue, or a custom gradient to show intensity
- Step 5: Add a chart title and adjust the year range, cell size, and font for readability
- Step 6: Click Export and download your calendar heatmap as PNG, PDF, SVG, JPEG, or WebP
Calendar Heatmap Best Practices & Tips
- Use a familiar green color scale (like GitHub contributions) unless you have a domain-specific reason to differ.
- Ensure each cell represents exactly one day — missing days should appear as empty (not zero) to be accurate.
- Calendar heatmaps reveal day-of-week patterns instantly — look for weekday vs weekend differences.
- Show at least 3 months of data; less than that does not provide enough context for pattern recognition.
- Add month and weekday labels on the axes so readers can pinpoint specific dates without counting cells.
- Annotate specific high-value or zero-value days with markers to highlight holidays, outages, or achievements.
- Calendar heatmaps are now a standard feature in fitness apps, coding platforms, and habit trackers.
- Use a diverging color scale when your data has both positive and negative values — for example, profit days in green shading versus loss days in red shading for financial tracking.
Common Calendar Heatmap Mistakes to Avoid
- Leaving gaps for days with no record. A missing 2026-03-14 row reads as a hole in the grid, not a zero, so fill absent days with 0 to distinguish a quiet day from a no-data day.
- Letting one extreme day stretch the color scale. A single 500-order Black Friday can push every ordinary 40-order day into the palest band; clip or cap the scale (e.g. at the 95th percentile) so normal variation stays visible.
- Aggregating to the wrong grain. A calendar heatmap needs one value per day, so summing multiple same-day records or feeding hourly timestamps without rolling them up to a daily total produces wrong cell colors.
Frequently Asked Questions
Can I show a full year?
Yes, the chart auto-layouts days into a 52-week grid like GitHub contributions.
What color scale works best?
Green scales (light to dark) are the most familiar from GitHub. Custom scales are also available.
Can I compare multiple years on one calendar heatmap?
Stack one heatmap per year vertically for direct comparison. ChartLoad also lets you set the year range to display multiple years in a continuous strip.
Related Chart Types
Ready-Made Calendar Heatmap Templates
Skip the blank canvas — open a free, editable Calendar Heatmap template, swap in your own data, and export. Browse all templates.
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