The following exercise is hypothetical. It considers a fully taxable, equity-financed investment with an asset price of one, no inflation or capital gains, no adjustment costs, and a constant required return and depreciation rate. It ignores credits, state taxes, loss limitations, interest deductibility, and other interactions. Its purpose is to isolate deduction timing and the financing return, not to reproduce the U.S. tax code.
Let r denote the required financing return, δ economic depreciation, τ the tax rate on the asset's operating return, and z the present value of depreciation deductions per unit of investment. Under these assumptions, a simplified annual pretax user cost is:
c = (r + δ) × (1 − τz) / (1 − τ).
The term 1 − τz is the acquisition cost after the value of deductions. Dividing by 1 − τ accounts for tax on the operating return. The return and depreciation term represents the annual resource cost of holding the capital under the simplified conditions. All rates in the formula use a common basis.
Set τ to 25% and δ to 10%. Compare z = 0.60 with immediate expensing, z = 1.00, at required returns of 5% and 6%.
| Required return r |
Deduction present value z |
Simplified user cost c |
| 5% |
0.60 |
17.0000% |
| 5% |
1.00 |
15.0000% |
| 6% |
0.60 |
18.1333% |
| 6% |
1.00 |
16.0000% |
For the first row, (0.05 + 0.10) × (1 − 0.25 × 0.60) / 0.75 = 0.17. With immediate expensing, the tax factor equals one under the stated assumptions, giving 0.15. Raising the required return by one percentage point then increases that user cost to 0.16. The combination of better deduction timing and a higher required return can therefore leave the user cost below its initial 0.17 level.
This is a conditional comparison. In practice, z itself can change with the discount rate when deductions occur in the future. Holding it fixed isolates a partial effect. A complete calculation would specify the deduction schedule and recompute its present value at each financing rate. A taxpayer unable to use deductions immediately would also require another treatment.