Accounting Retention Rate (Per-Unit) Formula
Learn how to calculate the percentage of starting customers, accounts, subscriptions, or other units retained during an accounting period.
Per-unit retention estimates how much of the starting unit base remains at the end of a period after removing units added during that period. It helps separate retention of an existing group from growth caused by new acquisition or activation.
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Per-Unit Retention Rate
Where:
Subtract new units from the ending total to estimate units retained from the starting group. Then divide that retained amount by the starting total and multiply by 100.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| beginningUnits - Units at Start of Period | The number of active customers, accounts, subscriptions, or other consistently defined units at the beginning of the period. | number |
| endingUnits - Units at End of Period | The total number of active units at the end of the same period, including units added during the period. | number |
| newUnits - New Units Added During Period | Units acquired, activated, or otherwise added during the period that are excluded from the retained-unit estimate. | number |
| retainedUnits - Retained Units | The estimated end-of-period units attributable to the starting group. | number |
| lostUnits - Units Lost | The estimated number of starting units that were not retained by the end of the period. | number |
Step-by-Step Calculation
Set the starting-unit baseline
Use the active-unit count at the first day of the accounting period as the comparison baseline.
beginningUnits
Remove new additions from the ending count
This isolates an estimated number of ending units from the starting group and prevents a negative retained-unit result.
retainedUnits = max(0, endingUnits - newUnits)
Calculate units lost
Compare estimated retained units with the beginning total to estimate how many starting units were not retained.
lostUnits = max(0, beginningUnits - retainedUnits)
Calculate the retention percentage
Divide retained units by beginning units and convert the result to a percentage.
retentionRate = (retainedUnits / beginningUnits) * 100
Calculate the churn percentage
Divide estimated lost units by beginning units to show the share of the starting group that was lost.
churnRate = (lostUnits / beginningUnits) * 100
Example: Customer retention for one quarter
Estimate retained customers
max(0, 950 - 100)
850 customers
Estimate customers lost
max(0, 1,000 - 850)
150 customers
Calculate retention rate
(850 / 1,000) * 100
85.0%
Calculate churn rate
(150 / 1,000) * 100
15.0%
Final Result
The estimated per-unit retention rate is 85.0%, with 850 starting customers retained and 150 customers lost.
Assumptions
- ✓Beginning, ending, and new-unit figures cover the same accounting period.
- ✓The same definition of a unit is used at the beginning and end of the period.
- ✓New units can be identified separately and are removed from the ending total.
- ✓Each unit is counted once in each period-end snapshot.
- ✓The calculation measures unit counts, not revenue, spend, or unit value.
Limitations
- !The formula cannot identify individual starting units without cohort-level records; it provides an operational estimate from aggregate counts.
- !Reactivations, acquisitions, mergers, migrations, and classification changes can affect the result.
- !A retention rate above 100% can indicate incomplete new-unit reporting or changes in how units are counted.
- !The result may differ from retention measures used in formal financial reporting or internal reporting policies.
Common Mistakes to Avoid
Using an ending-unit count from a different date range than the beginning-unit count.
Including new units in retained units instead of subtracting them from the ending total.
Counting reactivated units inconsistently as either new units or retained units.
Changing the definition of an active customer, account, or subscription between periods.
Comparing unit retention directly with revenue retention as though they measure the same outcome.
Related Formulas
Frequently Asked Questions
What is the per-unit retention rate formula?
Per-unit retention rate equals retained units divided by beginning units, multiplied by 100. Retained units are estimated as ending units minus new units.
How do you calculate retained units?
Subtract new units added during the period from total ending units. The calculator uses max(0, ending units minus new units) so the retained-unit estimate does not fall below zero.
How is per-unit churn calculated?
Per-unit churn equals estimated units lost divided by beginning units, multiplied by 100. Units lost equal beginning units minus retained units, with a minimum of zero.
Why is new business excluded from the retention formula?
New business increases the ending total but was not part of the opening group. Excluding it focuses the measure on the starting units that remained active.
Can unit retention exceed 100%?
Yes. If ending units less reported new units exceed beginning units, the estimate exceeds 100%. Review reactivations, acquisitions, data definitions, and new-unit classification when this occurs.
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