Add up delivery costs and overhead, choose a margin, then check how many sales you need. Start with time sheets, engagement scopes and invoice ageing. Each example below uses hypothetical values you can replace.
Which calculator should you use?
| Tool | What it answers | What to check |
|---|---|---|
| Target Margin Quote | Find a quote that retains the chosen margin after revenue-based commission. | Adding a commission percentage to cost does not preserve the target margin. Commission is based on the selling price. |
| Contribution per Sale | Find the amount a completed sale contributes toward fixed costs. | Contribution still needs to cover rent, management, software, and other fixed costs before there is net profit. |
These tools answer different questions and may use different units. Choose the tool that measures what you need; a larger result does not necessarily mean a better outcome.
Target Margin Quote
Find a quote that retains the chosen margin after revenue-based commission.
Quote = (itemised delivery costs + allocated overhead) ÷ (1 − margin − commission)
Show example inputs and result
| Staff hours cost | 200 |
|---|---|
| Software cost | 150 |
| Review time cost | 50 |
| Fixed overhead allocated to this client month | 100 |
| Target margin after commission | 25 % |
| Selling-price commission | 5 % |
Result: 714.2857 . Delivery cost 400; allocated overhead 100; commission 35.7143; retained contribution after assigned costs 178.5714.
Adding a commission percentage to cost does not preserve the target margin. Commission is based on the selling price.
Open target margin quoteContribution per Sale
Find the amount a completed sale contributes toward fixed costs.
Contribution = price − materials − hours × labour cost − other variable cost
Show example inputs and result
| Revenue per client month | 800 |
|---|---|
| Materials or purchased services | 250 |
| Delivery labour hours | 5 |
| Burdened hourly labour cost | 35 |
| Other variable cost | 50 |
Result: 325 .
Contribution still needs to cover rent, management, software, and other fixed costs before there is net profit.
Open contribution per saleUse the results in your plan
For a bookkeeping service business, review staff hours, software, and review time across the complete workflow. Use one consistent period and delivery unit: a client month. Compare the assumptions with recorded outcomes after delivery, then update the estimate.
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