Bookkeeping service Retainer Delivery Hours Available
Available hours = (retainer × (1 − margin) − other delivery costs) / hourly cost
Gather time sheets, engagement scopes and invoice ageing. Include staff hours, software, and review time. The starting figures are examples. Replace them with your own records.
Formula and worked example
Available hours = (retainer × (1 − margin) − other delivery costs) / hourly cost
| Input | Example |
|---|---|
| Monthly retainer fee | 3,000 |
| Non-labour monthly delivery cost | 300 |
| Target contribution margin | 40 % |
| Loaded delivery hourly cost | 45 |
| Calculated result | 33.3333 hours per month |
Choose reliable inputs
Account for delivery time, review work and when you expect to be paid for each engagement. For this bookkeeping service calculation, use time sheets, engagement scopes and invoice ageing and a consistent definition of one client month.
- Staff hours: include the portion belonging to this client month or reporting period, and record where the value came from.
- Software: include the portion belonging to this client month or reporting period, and record where the value came from.
- Review time: include the portion belonging to this client month or reporting period, and record where the value came from.
Use the same currency for every money input. Do not mix weekly costs with monthly revenue, or count the same expense in both an itemised cost and allocated overhead.
How many hours can a retainer support?
A negative answer means other costs already exceed the chosen cost envelope. Fixed overhead is not included unless entered.
What if this input changes?
If monthly retainer fee rises by 10%, this example changes by 4 hours per month. This shows the effect of one change; it does not predict what will happen.
Open the calculator, save your baseline, then change the input supported by the least reliable estimate in your records. Compare both scenarios before committing to a price or capacity promise.