NPV Guide 2026: Net Present Value Formula, Examples and Decisions
Table of Contents
The NPV Formula
NPV discounts every future cash flow to today and subtracts what you pay upfront. NPV > 0: do the project. NPV < 0: reject it. It is the single most theoretically sound investment criterion in finance.
Exclude sunk costs — the #1 NPV error in small business. Spent $40,000 on a failed prototype? That money is gone whether you proceed or not, so it has no place in the NPV calculation, which counts only future cash flows. Including sunk costs justifies throwing good money after bad; every struggling project suddenly "needs" to continue because of what's already spent. NPV is forward-looking by design — let it be.
Keep nominal and real consistent. Discounting nominal (inflation-included) cash flows with a real discount rate — or vice versa — understates or overstates value by 2-3% per year, compounded. A 10-year project mis-specified this way can swing $20,000+ on a $100,000 investment. Pick one lane: nominal cash flows with nominal rates (which include inflation expectations), or real with real. Mixing lanes is the quietest way to get NPV exactly wrong.
Worked Example: $100,000 Project
Project: Invest $100,000 today. Receive $30,000/year for 5 years. Discount rate 10%.
| Year | Cash Flow | Discount Factor | Present Value |
|---|---|---|---|
| 0 | −$100,000 | 1.000 | −$100,000 |
| 1 | $30,000 | 0.909 | $27,273 |
| 2 | $30,000 | 0.826 | $24,793 |
| 3 | $30,000 | 0.751 | $22,539 |
| 4 | $30,000 | 0.683 | $20,490 |
| 5 | $30,000 | 0.621 | $18,628 |
| NPV | $13,723 |
NPV = +$13,723 → accept. The project creates $13,723 of value above a 10% return hurdle.
Try an uneven-flows example: a $100,000 machine generating $20,000 / $30,000 / $40,000 / $50,000 / $60,000 over five years, plus $10,000 salvage value in year 5, discounted at 10%. Present values: $18,182 + $24,793 + $30,053 + $34,151 + $43,465 = $150,644. NPV ≈ +$50,600 — accept; the project creates over $50,000 of value above the hurdle. Notice how the back-loaded flows still contribute: year 5's $70,000 is worth $43,465 today, proving that distant cash isn't worthless, just discounted.
Never forget the depreciation tax shield. That $100,000 machine on 5-year straight-line depreciation generates $20,000/year in deductions; at a 24% tax rate that's $4,800/year of real cash savings. Present value at 10%: $4,800 × 3.791 = $18,197 — nearly a fifth of the investment returned through taxes alone. Add tax shields to operating cash flows before discounting; projects that look marginal pre-tax often clear the hurdle after shields.
Choosing the Discount Rate
- Corporate: Weighted average cost of capital (WACC) — often 8-12%.
- Personal: Your opportunity cost — what the money would earn elsewhere (e.g., 7% in index funds).
- Risk adjustment: Add 2-5% for risky cash flows.
Sensitivity check: at 15% discount, the same project's NPV falls to −$645 → reject. Always test two rates — the discount rate often decides the answer.
Build your discount rate with CAPM instead of guessing: 4.5% risk-free rate + 1.2 beta × 5.5% equity risk premium = 11.1% cost of equity. Blend with after-tax debt — say 6% debt × (1 − 0.24) = 4.56%, in a 60/40 equity-debt mix → WACC ≈ 8.5%. Your discount rate is a formula with observable inputs, not a vibe. Document each input so the rate survives scrutiny when the project underperforms.
Startup hurdles run far hotter: VCs routinely discount at 25-40%. At 30%, $1 million of year-5 cash flow is worth just $269,000 today — distant promises get crushed. That's why early revenue is gold for startups: every dollar pulled from year 5 into year 2 multiplies in present value. De-risk early and the appropriate discount rate falls; the valuation follows the risk, not the spreadsheet.
NPV vs IRR vs Payback
| Method | Strength | Weakness |
|---|---|---|
| NPV | Measures absolute value created | Needs a discount rate |
| IRR | Intuitive % return | Breaks with unconventional cash flows; reinvestment assumption |
| Payback | Simple, liquidity-focused | Ignores time value and post-payback flows |
When NPV and IRR conflict (different project scales), trust NPV — it measures dollars, not percentages.
When capital is limited, rank by profitability index, not raw NPV. Project A: $100,000 cost, $50,000 NPV. Project B: $40,000 cost, $45,000 NPV. NPV alone picks A — but PI (NPV ÷ cost) scores B at 1.125 versus A's 0.50 per dollar invested. With a $100,000 budget you could fund two B-type projects for $90,000 of NPV versus one A for $50,000. NPV measures total value; PI measures value per scarce dollar. Use the right tool for the constraint.
For different project lives, convert to Equivalent Annual Annuity: EAA = NPV ÷ annuity factor. A 5-year project with $30,000 NPV (factor 3.791) gives EAA $7,914; a 10-year project with $45,000 NPV (factor 6.145) gives EAA $7,323 — the shorter project wins despite the smaller NPV. Real-estate shortcut: cap rate ≈ discount rate minus growth, so a 6% cap with 2% growth implies roughly an 8% discount rate — a quick cross-check for property NPVs.
Frequently Asked Questions
Your opportunity cost — typically 6-8% (expected stock returns) for long horizons, or your mortgage rate for debt-payoff comparisons.
Yes — that is its strength. Discount each year's actual expected flow individually rather than averaging.
You earn exactly the discount rate — acceptable if that rate was your true hurdle, but with no margin for error.
Use nominal cash flows with a nominal discount rate, or real with real — consistently. Mixing them double-counts or ignores inflation.
For liquidity-constrained or highly uncertain environments, knowing 'when do I get my money back' has practical value NPV doesn't capture.