Earnings per share is one of the most widely referenced metrics in equity markets and one of the most commonly tested concepts in investment banking interviews. It connects a company's profitability to its share price through the P/E ratio, and it's the metric at the heart of accretion/dilution analysis in M&A.
What Is EPS?
Earnings per share measures the portion of a company's net income attributable to each outstanding share of common stock:
Basic EPS = Net Income / Weighted Average Shares Outstanding
If a company earns £100m of net income and has 50m shares outstanding, Basic EPS is £2.00.
The 'weighted average' part matters because share counts change throughout the year – if the company issues 10m new shares halfway through the year, the weighted average would be 55m (50m for the first half + 60m for the second half).
Basic vs Diluted EPS
Basic EPS uses only currently outstanding shares in the denominator.
Diluted EPS includes the impact of all potentially dilutive securities – stock options, restricted stock units (RSUs), convertible bonds, and convertible preferred stock. These securities could convert into common shares, diluting existing shareholders.
Diluted EPS = Net Income (adjusted) / (Weighted Average Shares + Dilutive Securities)
For stock options, the dilutive impact is calculated using the Treasury Stock Method: assume all in-the-money options are exercised, the company receives the exercise price as cash, uses that cash to buy back shares at the current market price, and the net new shares are added to the denominator.
For convertible bonds, you use the If-Converted Method: assume the bonds convert to equity, add the new shares to the denominator, and add back the after-tax interest expense to the numerator (since the company would no longer be paying interest on the converted bonds).
'Why do we care about diluted EPS more than basic EPS?' Because diluted EPS reflects the potential impact of all securities that could become common shares. It gives a more conservative (and realistic) picture of per-share earnings. In M&A, accretion/dilution analysis always uses diluted EPS. An interviewer who asks about EPS almost certainly means diluted EPS.
How EPS Connects to Valuation
The P/E ratio – the most widely quoted equity valuation multiple – is simply:
P/E Ratio = Share Price / EPS
If a company trades at £30 per share and earns £2 of diluted EPS, its P/E ratio is 15x. This means investors are paying £15 for every £1 of current earnings.
P/E is useful for quick relative valuation: if Company A trades at 15x earnings and Company B at 25x, the market expects higher growth from Company B. But P/E has significant limitations – it's affected by capital structure (interest expense reduces EPS), tax rates, and one-time items, all of which make cross-company comparison imperfect.
'Is a lower P/E always better?' No. A low P/E could mean the stock is undervalued, or it could mean the market expects earnings to decline. Cyclical companies often have low P/Es at cycle peaks (high earnings, expected decline) and high P/Es at cycle troughs (depressed earnings, expected recovery). Context matters enormously.
EPS Growth and Why It Matters
Investors and analysts focus heavily on EPS growth because it's the primary driver of share price appreciation over time. Companies grow EPS through some combination of revenue growth, margin expansion, and share buybacks (which reduce the denominator).
This is why share buybacks are so popular: even if net income is flat, reducing the share count through buybacks mechanically increases EPS. A company earning £100m with 50m shares has £2.00 EPS. Buy back 5m shares, and EPS rises to £2.22 without any improvement in underlying profitability.
EPS in M&A: Accretion and Dilution
When Company A acquires Company B, the combined entity will have different EPS than either standalone company. If the deal is funded with stock (issuing new shares to pay for the acquisition), the acquirer's share count increases, which can dilute EPS.
A deal is accretive if the combined EPS exceeds the acquirer's standalone EPS. A deal is dilutive if the combined EPS falls below the acquirer's standalone EPS.
Whether a stock deal is accretive or dilutive depends on the relative P/E ratios: if the acquirer's P/E is higher than the target's, a stock deal is typically accretive. If the acquirer's P/E is lower, it's typically dilutive.
Common Interview Questions
'Walk me through the EPS formula.' Net Income divided by diluted weighted average shares outstanding. Include the impact of options (Treasury Stock Method) and convertible securities (If-Converted Method) in the share count.
'If a company does a 2-for-1 stock split, what happens to EPS?' EPS is cut in half because the share count doubles. But the stock price also halves, so the P/E ratio is unchanged. A stock split has no economic impact.
'How can a company increase EPS without improving operations?' Share buybacks (reduce denominator), one-time gains (inflate numerator temporarily), or acquisitions at favourable P/E ratios (accretive deals).
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