How to measure customer purchase frequency

Purchase frequency is how often a customer buys from you. For trades and service firms it is usually measured from invoice dates, not website sessions. Spotting customers who still buy—but less often—is one of the highest-ROI reactivation moves.

How to measure it

1. List invoice dates per customer (exclude voided / drafts).
2. Compute gaps between consecutive invoices; use the median gap as their cadence.
3. Compare recent gaps (or time since last invoice) to that median.
4. Require a minimum history (e.g. three prior invoices) before calling a slowdown “real.”

What “slowing down” looks like

Customer       Prior cadence   Recent signal
Northvale      ~90 days        210 days since last
Elm Service    ~45 days        last three gaps 60–80 days
One-off Co     n/a             skip — only one invoice

Common mistakes

• Treating every contact with no invoice in 90 days as lapsed.
• Ignoring seasonality (spring plant, winter boiler).
• Mixing quotes and invoices when counting “purchases.”
• Acting on two-invoice histories as if they were a cadence.

How Spearmint helps

Mint includes questions such as which returning customers are buying less frequently, executed against an immutable commercial snapshot with evidence links. Low-confidence patterns stay uncertain instead of silently qualifying.