Formula
Customers upgrading / Total existing customers x 100
How to measure
Divide the count of customers who moved to a higher plan tier during the period by the total customer base at the start of the period.
Why track it
Upsell rate is one of the cheapest levers for revenue growth, since it targets an already-trusting customer relationship.
Example
A company upgrades 40 of its 1,000 existing customers to a higher tier this quarter, a 4% upsell rate.