ACCA AFM APV 2026: The WACC Mistake That Double-Counts Your Tax Shield
If you discount the project at WACC and then add the tax shield, you've counted the debt benefit twice — and the examiner will take the marks back. APV exists precisely to keep the project and its financing apart. Mix them and the whole method collapses.
Why APV is a separate method
APV splits the decision in two. First you value the project as if it were all-equity financed — the base case NPV. Then you add the financing side effects debt brings: the tax shield, issue costs, and any subsidised loan benefit. The two parts use different discount rates on purpose, and that is exactly where AFM candidates come unstuck.
The base case must be discounted at the ungeared (asset) cost of equity, Keu — found from the M&M formula or by ungearing an asset beta. It is not WACC. WACC already bakes in the tax benefit of debt, so if you discount at WACC and then bolt the tax shield on top, you double-count. The financing side effects are then discounted separately, usually at the pre-tax cost of debt (often the risk-free rate), because those cash flows carry debt-level risk, not project risk.
When to reach for APV over NPV
APV earns its keep when the capital structure changes materially because of the project, or when the financing is unusual — a subsidised loan, significant issue costs, or complex tax-relief timing. In a stable structure, ordinary NPV at WACC is fine. AFM questions signal APV by handing you a subsidised rate or a debt issue with costs attached. Spot the signal and switch methods.
Worked example: the double-count, fixed
A four-year project generates $50,000 a year after tax. Keu is 11%; WACC is 9%. The firm raises $200,000 of debt at a 5% market rate, tax at 25%.
Wrong: discount the operating flows at WACC 9% (4-year annuity factor 3.240) → $50,000 × 3.240 = $162,000, then also add the tax shield. The 9% rate already rewarded the debt, so the shield is counted twice.
Right (APV): base case at Keu 11% (factor 3.102) → $50,000 × 3.102 = $155,100. Tax shield = $200,000 × 5% × 25% = $2,500 a year, discounted at the 5% pre-tax cost of debt (factor 3.546) → $8,865. APV = $155,100 + $8,865 = $163,965 before the initial outlay.
The two answers are close here by design — but the wrong route would keep adding the shield on top, inflating the figure and signalling to the marker you don't understand what WACC contains.
What to do
1. Lock the base case to Keu. Ungear the beta (or use M&M) first, every time. If you've typed WACC into the base-case discount line, you've already lost the method marks.
2. Discount each financing effect at its own rate. Tax shield and subsidised-loan savings go at the pre-tax cost of debt or risk-free rate — not Keu, not WACC.
3. Don't forget issue costs. They reduce the financing benefit, and if they're tax-deductible you gross them up for the relief. Candidates routinely drop them entirely.
Bottom line
AFM sits around a 40% pass rate, and Section A's investment question is where it's won or lost. APV is generous to anyone who keeps project and financing in separate columns. Pick Keu for the base case, the cost of debt for the side effects, and never let WACC touch an APV answer.