To calculate the after-tax incremental cash flow of a project, you tally only the cash inflows and outflows that exist because the project exists, subtract the taxes those flows generate, and add back non-cash deductions like depreciation. The result is the real money the project puts in or takes out of the company in each period, which is what capital budgeting decisions actually turn on. The work breaks into four pieces: the year-zero outlay, the annual operating cash flows during the project’s life, the terminal-year recovery, and a discipline for keeping non-incremental numbers out of all three.
The Core Formula
Every year of operating cash flow follows the same equation:
Operating Cash Flow = (Revenue − Expenses − Depreciation) × (1 − Tax Rate) + Depreciation
Revenue and expenses are the incremental figures caused by the project. Depreciation is subtracted before tax because it reduces the tax bill, then added back because no cash actually left the business when it was recorded. That add-back is the depreciation tax shield in action.
Step 1: Screen Every Number Through the Incremental Test
Before any arithmetic, decide what belongs in the model. A cash flow is incremental only if it would not occur without the project. Four categories cause most of the mistakes.
Sunk costs stay out. A $20,000 engineering study completed six months ago is gone whether you approve the project or not. It feels relevant because it relates to the project, but it changes nothing about future cash and does not belong in the analysis.
Opportunity costs come in. If your company owns a warehouse it could lease for $10,000 a month and instead uses it for a new assembly line, that forgone rent is a real cost of the project. The project effectively pays for the space by eliminating revenue the company would otherwise collect.
Cannibalization comes in. If launching a lighter version of your flagship product reduces the flagship’s revenue by $200,000 a year, subtract that amount from the new product’s projected cash flows. Ignoring it overstates the project by pretending the lost sales don’t exist.
Interest expense stays out. Interest is a real cash payment, but the cost of financing is already captured in the discount rate you apply later, typically the weighted average cost of capital. Putting interest in the cash flows and then discounting at a rate that also reflects borrowing costs counts the same expense twice.
Step 2: Build the Year-Zero Outlay
The initial outlay is the total cash leaving the company the moment the project launches, entered as a negative number at time zero.
Start with the purchase price of the asset. Add every cost required to get it operational: freight, installation labor, site preparation, and testing. These aren’t incidentals; they become part of the asset’s depreciable base, which is the starting figure used to calculate depreciation deductions over its useful life.1Internal Revenue Service. Topic No. 703, Basis of Assets
Then add the change in net working capital the project demands. A manufacturing project might need $50,000 in raw materials inventory and $15,000 in additional cash to cover daily operations before revenue starts flowing, offset by any increase in accounts payable from suppliers extending credit. The net figure is a cash outflow at year zero. It isn’t gone permanently; the money comes back at the end of the project when inventory is sold off and receivables are collected.
Step 3: Calculate Each Year’s Operating Cash Flow
Once the project is running, work through three steps for each year:
- Earnings before interest and taxes (EBIT): incremental revenue minus incremental operating expenses minus depreciation. Depreciation belongs here so the tax figure comes out right, not because cash left the business.
- Taxes: multiply EBIT by the applicable tax rate. The federal corporate rate is 21 percent. Most states add a corporate income tax ranging roughly from 2 to 12 percent, though a handful of states impose none. Your effective combined rate depends on where the project operates.
- Add depreciation back: since it reduced EBIT but never left the bank account, put it back to reach actual cash generated.
Working capital doesn’t only move at launch. If year-three revenue is higher than year-two revenue, the project probably needs more inventory and will carry higher receivables. That increase is a cash outflow in year three that reduces free cash flow. If working capital requirements shrink in a later year, the freed-up cash counts as an inflow.
Depreciation and the Tax Shield
Depreciation is a non-cash accounting deduction, but every dollar of it reduces taxable income, which reduces the tax bill, which keeps real cash in the company. At the 21 percent federal rate, a $100,000 depreciation deduction saves $21,000 in taxes. That $21,000 is the tax shield, and the method you use to depreciate the asset changes how quickly it arrives.
MACRS Recovery Periods
Most business assets are depreciated under the Modified Accelerated Cost Recovery System, which assigns each asset to a recovery period based on its class life. Common categories include five-year property for computers and office equipment, seven-year property for furniture and most machinery, and 27.5 or 39 years for residential rental and commercial buildings, respectively. The standard method for five- and seven-year property uses a 200 percent declining balance approach that front-loads deductions into the early years, then switches to straight-line when that produces a larger deduction. The half-year convention assumes each asset was placed in service at the midpoint of the tax year regardless of the actual purchase date, so only half a year’s depreciation is claimed in both the first and last years.2Office of the Law Revision Counsel. 26 U.S. Code 168 – Accelerated Cost Recovery System
Bonus Depreciation and Section 179
Two provisions let a business pull the tax shield forward. Bonus depreciation, restored to 100 percent for property placed in service in 2026 under the One Big Beautiful Bill Act, allows the full cost of qualifying new or used equipment to be deducted in the first year. For a $500,000 machine, that produces a $105,000 tax shield in year one instead of spreading it across five or seven years.
Section 179 expensing offers a similar first-year write-off with a cap. For 2026, the maximum deduction is $2,560,000, and the benefit begins phasing out once total equipment purchases exceed $4,090,000. Section 179 is limited to the business’s taxable income for the year, so it cannot create or increase a net operating loss. Bonus depreciation can.
The choice matters for the model. Under standard MACRS, the tax shield trickles in over years. Under 100 percent bonus depreciation, the whole shield lands in year one, which raises the present value of the project’s cash flows substantially. If your model assumes standard MACRS but the company will actually elect bonus depreciation, you’ll understate the project’s value.
Step 4: Add the Terminal Year Items
The final year includes everything from the normal operating cash flow calculation plus two additions: the after-tax salvage value of the asset and the recovery of net working capital.
After-Tax Salvage Value
When you sell or scrap the asset, the sale price is a cash inflow, but taxes hinge on the difference between sale price and book value. If a machine has been depreciated to a $10,000 book value and sells for $15,000, the $5,000 gain is taxable. At 21 percent federal, tax on the gain is $1,050, leaving a net cash inflow of $13,950.3Internal Revenue Service. Sale of a Business
A loss cuts the other way. If that same machine sells for $6,000 against a $10,000 book value, the $4,000 loss generates a tax benefit worth $840 at the federal rate, making the effective inflow $6,840. Assets fully depreciated to zero that sell for any amount trigger a gain on the entire sale price.
Working Capital Recovery
The net working capital invested at the start flows back in the terminal year as inventory is liquidated, receivables are collected, and project-related payables are settled. The recovery equals the cumulative working capital the project consumed. It isn’t taxable because it’s a return of the company’s own capital, not income.
Putting the Timeline Together
The full schedule looks like this:
- Year 0: negative cash flow equal to the asset purchase price (with all costs to make it operational) plus the initial net working capital investment.
- Years 1 through N−1: annual operating cash flows, adjusted for any year-to-year changes in net working capital.
- Year N: that year’s operating cash flow plus after-tax salvage value plus recovery of all net working capital.
From there the cash flows get discounted at the company’s required rate of return to produce a net present value or an internal rate of return. Where most analyses go wrong isn’t the discounting or the arithmetic; it’s the inputs. Optimistic revenue projections, ignored opportunity costs, forgotten cannibalization, or the wrong depreciation assumption can each swing a project from value-creating to value-destroying. The habit that keeps the analysis honest is forcing every number through the same question: does this cash flow change because of this specific project?