The short answer is that mortgage rates are a special overlay designed to provide economic context, not a second chart metric.
Our charts are built to display one primary market metric per chart to keep trends clear and easy to interpret. Mortgage rates are the one exception because they’re an external economic indicator that affects all housing metrics, rather than being another measure of market activity.
Technically and conceptually, mortgage rates:
- Use a standardized national data source
- Follow a consistent scale and update pattern
- Are meant to provide context, not comparison
That allows them to be added as an overlay without changing how the chart itself is calculated or scaled.