Why must synergies, new interest expense, and foregone interest on cash all be tax-affected before they hit pro-forma net income? Give the after-tax value of $60M of pre-tax synergies at a 25% rate.

What the merger-model test is actually testing

Accretion/dilution is the most conceptual of the modeling tests: the arithmetic is light, but the reasoning is dense, and interviewers use it to see whether you understand who bears the cost of an acquisition and through which channel. Three things are graded:

1. Do you reason from the consideration mix? Everything flows from cash-vs-debt-vs-stock. A strong candidate, handed a deal, immediately asks or assumes the mix and predicts the direction before building: 'It's all-stock and we trade at 20x buying a company at 15x; I'd expect this to be accretive, and I'll confirm with the model.' Predicting direction from the P/E comparison, then verifying, is the single strongest signal.

2. Do you tax-affect correctly? Synergies, new interest expense, and foregone interest income are all pre-tax and must be run through (1 − t). Candidates who add pre-tax synergies straight to net income, or forget that interest is tax-deductible, reveal they've memorized a template without understanding the income statement. Say 'after-tax' out loud each time.

3. Can you find the breakeven? The reflex senior follow-up to any accretion/dilution answer is 'how much synergy do you need to break even?' or 'at what premium does it flip?' A candidate who can solve for the breakeven (set pro-forma EPS equal to standalone EPS and back out the driver) demonstrates they understand the model as a system of levers, not a fixed output.

The meta-signal: direction first, magnitude second, breakeven third. State whether the deal is accretive or dilutive and why in one sentence, give the approximate magnitude, then volunteer the breakeven. That sequence is what a deal team actually needs and is exactly how a strong analyst frames it in a live pitch.

The traps that blow up a merger model

Trap 1: Forgetting to tax-affect synergies and interest. The most common error. Pre-tax synergies of $50M at a 25% tax rate add only $37.5M to net income; new interest of $40M reduces net income by only $30M after tax. Adding or subtracting the pre-tax figures directly corrupts the accretion number.

Say it out loud: "Synergies, new interest, and foregone interest all hit pre-tax income, so they flow to net income at one minus the tax rate. $50M of pre-tax synergies is $37.5M after tax at a 25% rate."

Trap 2: Getting the all-stock P/E rule backwards. Candidates blank on whether a high-P/E or low-P/E acquirer is the accretive one in an all-stock deal.

Say it out loud: "In an all-stock deal, if the acquirer's P/E is higher than the P/E it pays for the target, the deal is accretive: you're financing the purchase at your own low earnings yield and buying a higher earnings yield. High-P/E buying low-P/E is accretive."

Trap 3: Confusing the target's standalone P/E with the P/E paid. Accretion depends on the P/E you pay (offer price including the control premium), not the target's unaffected trading P/E. A control premium raises the effective P/E paid and pushes toward dilution.

Say it out loud: "What matters is the P/E I pay, which includes the premium, not the target's screen P/E. A 30% premium raises the effective purchase P/E, so a deal that looks accretive at the unaffected price can be dilutive once I pay the premium."

Trap 4: Ignoring foregone interest on cash used. Cash isn't 'free' financing: using it means giving up the interest income that cash was earning. Candidates model new debt interest but forget the opportunity cost of deploying cash.

Say it out loud: "Cash consideration has a cost too: the after-tax interest income the acquirer forgoes on that cash. It's usually a low yield, which is why cash deals are typically accretive, but it's not zero."

Trap 5: Mixing GAAP EPS and cash EPS. New intangible amortization from purchase accounting dilutes GAAP EPS but is non-cash. Candidates report one number without flagging which, or forget that acquirers highlight cash EPS to make deals look accretive.

Say it out loud: "Purchase accounting creates new intangible amortization that dilutes GAAP EPS but is non-cash, so I'd show cash EPS as well, which adds back deal amortization. A deal can be GAAP-dilutive but cash-accretive, and management will lead with the cash number."

Trap 6: Reporting accretion without the breakeven. Candidates state 'it's 2% accretive' and stop, missing that the interviewer's next question is always 'what would flip it?'

Say it out loud: "It's about 2% accretive. To break even I'd need synergies to fall to roughly [X], or the premium to rise above [Y]%; that's the cushion the deal has."