In this example, increasing equipment cost from 200 to 220 changes the result from 714.2857 to 742.8571 . All other inputs stay the same.
Try this with your own numbersFormula and worked example
Quote = (itemised delivery costs + allocated overhead) ÷ (1 − margin − commission)
| Input | Example |
|---|---|
| Equipment cost | 200 |
| Subcontract work cost | 150 |
| Site access cost | 50 |
| Fixed overhead allocated to this installation | 100 |
| Target margin after commission | 25 % |
| Selling-price commission | 5 % |
| Calculated result | 714.2857 |
Delivery cost 400; allocated overhead 100; commission 35.7143; retained contribution after assigned costs 178.5714.
Choose reliable inputs
Plan materials, travel and crew time before committing to a price. For this solar installation calculation, use a completed job sheet, supplier quotes and a crew schedule and a consistent definition of one installation.
- Equipment: include the portion belonging to this installation or reporting period, and record where the value came from.
- Subcontract work: include the portion belonging to this installation or reporting period, and record where the value came from.
- Site access: include the portion belonging to this installation 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 should commission change my quote?
Adding a commission percentage to cost does not preserve the target margin. Commission is based on the selling price.
Allocate overhead once; target margin and commission together must be below 100%.
What if this input changes?
If equipment cost rises by 10%, this example changes by 28.5714 . 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.