Private Equity puzzles, solved step by step

11.5% compounded monthly pays more: an effective 12.13% against 12.00%. Monthly compounding pays 0.958% each month, and each payment then earns interest for the rest of the year. Over twelve months that interest on interest adds about 0.63 points to the 11.5% headline. Compare effective annual rates, never headline rates with different compounding.

Why can a lower headline rate pay more?

Imagine two jobs paying the same annual salary, one paid monthly and one in a single lump in December. The monthly earner can put January's pay in a deposit and earn on it for eleven months. The more often interest is paid, the sooner it starts earning interest of its own, so the effective rate rises above the headline rate. 11.5% paid monthly is 0.958% a month, and each month's interest joins the balance that earns the next month's.

How do you estimate the extra without a calculator?

Use the second term of the expansion. Compounding r over n periods adds roughly r squared times (n minus 1) over 2n on top of r, which for 11.5% monthly is about 0.0132 x 11/24, or 0.61 points. So 11.5% plus about 0.6 is roughly 12.1%, enough to beat 12%. The exact figure is 12.13%. A quicker sanity check: continuous compounding is the ceiling, e to the 0.115, which is 12.19%, and monthly sits just below it.

Where does this show up on a private equity desk?

In debt terms and in returns reporting. Loan margins, PIK interest and preferred returns are quoted with different compounding conventions, and comparing them on headline rates is the same mistake as answering 12% here. A PIK note that compounds quarterly costs more than its headline suggests. Fund returns quoted as an IRR are already annual effective rates, which is why they can be compared across funds with different cash flow timing.

The score is 25 today, and at 25% growth the margin must reach 15%. The Rule of 40 adds revenue growth and profit margin: 35 plus minus 10 is 25, well short of 40. If growth slows to 25%, the margin has to be 40 less 25, or 15%. That is a swing of 25 points of margin, from minus 10% to plus 15%, just to hold the bar.

What is the Rule of 40 actually measuring?

Think of a young restaurant that can either open new branches fast and lose money doing it, or open slowly and keep every branch profitable. Either can be healthy; losing money while also growing slowly is not. The Rule of 40 adds growth and margin so that a software company can trade one for the other, and treats a combined score of 40 or more as a sign of a healthy balance. Growth of 35% and a margin of minus 10% score 25, which says the company is spending more on growth than the growth is earning.

Why does slowing growth make the margin job so large?

Because the score falls point for point. Losing 10 points of growth drops the score from 25 to 15 if nothing else moves, so the margin has to cover both the existing 15-point shortfall and the 10 points just lost. That is 25 points of margin. In practice it means cutting sales and marketing spend that was buying the growth, which is often exactly what happens when a buyout fund takes over a software business: growth slows by choice and margin is rebuilt.

What should you say about the rule's limits?

That it is a heuristic, not a law. Different investors use different margin definitions, EBITDA, operating or free cash flow, and the same company can pass on one and fail on another. The rule also treats a point of growth and a point of margin as equal, which is untrue for a small company where growth compounds into a much larger future business. Use it to frame the trade-off, then look at what is driving each side: retention, sales efficiency and gross margin.

About 684, and leverage of about 9.8x. Each year 11% is added to the balance rather than paid: 500 grows to 555, then 616, then 683.8. Add the 300 of other debt and total debt is 984 against EBITDA of 100, so 9.8x, up from 8.0x today. The company has kept 150 of cash over the three years and taken on 184 of extra debt to do it.

What does toggling to PIK actually do?

Think of a credit card where you can skip the monthly payment and let the interest be added to the balance. Nothing leaves your account this month, but next month's interest is charged on a bigger number. A toggle noteA bond or loan whose issuer can choose each period to pay interest in cash or to add it to the principal, usually at a higher rate for the in-kind option. lets the borrower choose that every period, and the price of choosing it is a higher rate charged on a balance that compounds. Here the cash option costs 50 a year. The PIK option costs 55 in year one, and because that 55 is added to the note, 61.05 in year two and 67.77 in year three.

How does the leverage climb, year by year?

Start at 800 of debt on 100 of EBITDA, 8.0x. After year one the note is 555 and total debt 855, so 8.55x. After year two the note is 616.05 and leverage 9.16x. After year three it is 683.82 and leverage 9.84x. Because EBITDA is flat, every unit the note accretes is a unit of leverage with no new earnings to carry it, and the ratio rises by almost two turns in three years without the business doing anything. That is the whole point of the question: PIK is deferred cash, not free cash, and it is deferred at a compounding rate.

When is toggling sensible, and what should you add?

When the cash has a better use than paying interest: a short period of heavy investment, or a downturn the company expects to come out of. The toggle buys time at a known price, and the question for the lender and the sponsor is whether the EBITDA that eventually has to carry 984 of debt will be there when the time runs out. Say the things the simple version leaves out: the 1-point premium over the cash coupon is what the lender charges for the option, PIK interest is often still a tax deduction even though no cash moves, and a 9.8x company usually needs an equity cure, a sale or growth, because refinancing at that level is hard.

About Rs 49.6 crore off the price, but a cut is the weaker fix. Expected damages are 30% x 200 = Rs 60 crore, payable in two years, so 60 / 1.1^2 is Rs 49.6 crore today. A price cut is fair on average yet leaves you Rs 200 crore exposed if the case is lost. A specific indemnity from the seller backed by an escrow moves the bad branch to the seller instead.

How do you put a number on something that may never happen?

A shopkeeper who knows that 3 in 10 customers return a gadget within the warranty sets aside money for returns before counting profit. A contingent liability is priced as chance times cost, then discounted for time: here 0.3 x 200 = Rs 60 crore, and two years at 10% brings it to Rs 49.6 crore. That is the average cost across all the ways the case could end, in today's money.

Why is a price cut not the best answer?

Because a buyer does not live the average; it lives one branch. Cut the price by 49.6 and lose the case, and you have paid for a Rs 200 crore liability with a Rs 49.6 crore discount. A specific indemnityA promise by the seller to reimburse the buyer for one named liability, here the lawsuit, if it costs money after completion. puts the bad branch back with the seller, who knows the case best. Backing it with an escrow, part of the price held back until the case ends, makes sure the money is there to collect.

Say the trade-offs. Sellers dislike escrows because cash is locked up, so expect to give something back, perhaps a smaller cut or a cap on the indemnity. Warranty and indemnity insurance usually excludes known issues like this one, so check the policy before relying on it. And the 30% is itself an estimate: ask the legal team how they reached it, because the answer moves one for one with it.

2.5x and an IRR of about 20%. Entry EV is 50 x 8 = 400, half debt, so equity is 200. Exit EV is 75 x 8 = 600, and debt has fallen from 200 to 100, so exit equity is 500. 500 over 200 is 2.5x. Over five years that is about 20% a year, since 1.2 to the fifth is about 2.49.

What is the fastest way to do this in your head?

Buy a flat for Rs 40 lakh with a Rs 20 lakh loan. Five years later it is worth Rs 60 lakh and you have paid the loan down to Rs 10 lakh. Your stake went from Rs 20 lakh to Rs 50 lakh. Every paper LBO is two balance sheets, entry and exit, and the answer is exit equity over entry equity, where equity is EV less debt each time. Write the four numbers, subtract twice, divide once.

How do you get the IRR without a calculator?

Carry three anchors for a five-year hold. 2x in five years is about 15% a year, 2.5x is about 20%, and 3x is about 25%. 1.2 to the fifth is 1.2 x 1.2 = 1.44, then 1.73, 2.07 and 2.49, so 2.5x is a touch over 20%: 20.1%. Saying the anchor and then the check sounds far more assured than reaching for a formula.

Then split the gain, because the interviewer will ask where the return came from. EBITDA rose 25 at a constant 8x, adding 200 of value; cash flow repaid 100 of debt; the multiple did not move, so it added nothing. The limitation: the sums ignore fees at entry and any cash left on the balance sheet at exit, both of which a real model would carry.

Choose levered free cash flow, and Company A is the cheaper one. Both cost 9.0x EBITDA, but A keeps 90 after capex and B only 50, so the same 900 buys cash at 10.0x in A and 18.0x in B. After 25% tax the gap holds at 13.3x against 24.0x. Levered free cash flow is the one number that has already paid for capex, working capital, interest and tax: it is what an owner can actually take out.

What does EBITDA leave out that matters here?

Picture two taxis, each bringing in Rs 1 lakh a month after fuel and the driver. One is new and needs little upkeep; the other is old and eats half its takings in repairs. Before repairs they look identical, and nobody would pay the same for both. EBITDA is earnings before the business pays for the assets it uses up, so two companies with equal EBITDA can leave their owners very different amounts of cash. Company B spends half its EBITDA just to keep running.

Why levered free cash flow rather than EBIT?

EBIT does subtract depreciation, which here happens to equal capex, so EBIT would rank the two correctly. But depreciation is an accounting estimate of past spending, not the cash going out this year, and it ignores working capital, interest and tax. Levered free cash flow is the only one of the three that is cash in the owner's hand after every claim ahead of the owner has been paid. Assume no debt and depreciation equal to capex: A's free cash flow is 100 less tax of 22.5 less capex of 10, which is 67.5; B's is 37.5.

What is the limit of your answer?

Say two things. First, one year of free cash flow can be lumpy: a big capex year or a working capital swing can make a good business look expensive. With a single period of data, levered free cash flow is the most honest number, but it is also the noisiest. Second, levered cash flow belongs to the equity, so you compare it with equity value, not enterprise value. In this example there is no debt, so the two are the same; with debt you would divide by equity value instead.

About 9 crore tyres a year, on the assumptions stated. Take about 20 crore two-wheelers in use, each riding about 7,000 km a year on 2 tyres: that is 2.8 lakh crore tyre-kilometres. If a tyre lasts about 30,000 km, roughly 9.3 crore tyres wear out each year. Tyre life is the sensitive input: 20,000 km gives 14 crore and 40,000 km gives 7 crore.

Why start from the bikes on the road rather than new sales?

Think of how many toothbrushes a household buys. It depends on how many people live there and how often a brush wears out, not on how many babies were born this year. A replacement market is sized off the installed base, the stock in use, multiplied by how fast each unit wears out. New two-wheelers arrive with tyres already fitted at the factory, which is a separate market sold to manufacturers, so counting new sales here would mix two different customers.

How do you defend each assumption out loud?

Say where each number comes from and how you would check it. Registered vehicle counts overstate the bikes in use, because scrapped vehicles stay on the register, so cut the registered figure down and say you are doing so. Seven thousand km is about 20 km a day, a commute and errands. Then run the cross-check a rider can judge: at 7,000 km a year a 30,000 km tyre lasts about four years, which sounds right for a commuter bike. All three inputs are illustrations to be confirmed against current industry data, not facts.

Close by naming the input you would research first. Tyre life halves or doubles the answer across a plausible range, and rear tyres wear faster than front ones, so a sharper version splits the two. A sponsor looking at a tyre retailer would care about exactly that split, because the rear tyre is the more frequent purchase.

Levered free cash flow is 92.5. EBITDA is 250. Take off D&A of 40 and interest of 60 to get pre-tax profit of 150, tax of 37.5 and net income of 112.5. Add back the 40 of D&A because it is not cash, then subtract capex of 50 and the 10 of working capital the growth absorbs. What remains, 92.5, is cash the owners could take out.

Why does depreciation come off and then go back on?

Think of a delivery van bought last year. Each year the accounts charge a slice of its cost as depreciation, but no money leaves the business that year: the van was paid for already. Depreciation reduces taxable profit, which saves real tax, but it is not a cash payment, so it is subtracted to work out tax and then added back to reach cash. The cash cost of assets enters through capex instead, here 50, which is more than the 40 of depreciation because the business is growing.

What makes it levered, and why does a buyout investor want that version?

Levered means after interest: the lenders have been paid. Levered free cash flow is the cash left for the equity holders after the lenders, the taxman and the business's own reinvestment, which is exactly the cash that repays debt in a buyout. Check it a second way from EBITDA: 250 less 60 less 37.5 less 50 less 10 is 92.5. The limit worth saying: working capital is modelled here as 10% of growth, and a real business can swing by far more in a single year.

The rule of 72 gives 36%; the exact IRR is about 41.4%. Eight times is three doublings, so the money doubles every two years, and 72 divided by 2 is 36. The exact rate is 8 to the power one sixth, which is the square root of 2, so the IRR is 1.414 minus 1, 41.4%. The rule runs low because it is tuned for rates near 8%.

How does the rule of 72 apply to a multiple bigger than 2?

Think of folding a sheet of paper: each fold doubles the thickness, so eight layers is three folds. Any money multiple that is a power of 2 is a count of doublings, and once you know the years per doubling, the rule of 72 gives the rate. Eight is 2 x 2 x 2, so six years hold three doublings of two years each. The rule says a doubling every two years needs 72 over 2, which is 36% a year.

How do you get the exact answer with a basic calculator?

You need the sixth root of 8. Split it: the sixth root is the square root of the cube root, and the cube root of 8 is 2, so the answer is the square root of 2. One press of the square root key gives 1.414, an IRR of 41.4%. Without a square root key, use trial and error: 1.4 squared is 1.96, and 1.96 cubed is about 7.53, a little short of 8, while 1.42 to the sixth is about 8.20, a little over. The answer sits between 40% and 42%.

Then say why the rule ran low. The rule of 72 is built around rates near 8%; the higher the rate, the bigger the number you should divide into. For a two-year doubling the exact rate implies a numerator of about 83, not 72. Checking the shortfall out loud, 36% for six years gives only 6.33x, shows the interviewer you know the rule's limit.

Break-even is Rs 5,000 a passenger; a 10% margin on revenue needs about Rs 5,556. A 2-hour flight costs 2 x Rs 3.6 lakh, Rs 7.2 lakh. An 80% load factor fills 144 of 180 seats, so each passenger must cover Rs 7.2 lakh / 144, Rs 5,000. For cost to be 90% of revenue, divide by 0.9, not multiply by 1.1, which gives about Rs 5,556.

Why divide by passengers and not by seats?

Think of a shared taxi to the airport that costs Rs 1,000 whether four people ride or two. If only two turn up, each pays Rs 500, not Rs 250. A flight costs the same to operate with empty seats, so the fare has to be set on the seats that are actually sold. That is why the load factor sits at the centre of airline economics: at 80%, every paying passenger carries a quarter of an empty seat.

What would you ask the interviewer for next?

In this format you can ask for more data, and asking well scores points. The two inputs that move the answer most are the load factor and what is inside the cost per hour, because fuel and aircraft leases dominate it. At a 70% load factor the break-even rises to about Rs 5,714. You might also ask about ancillary revenue, bags and seats, which lets the base fare sit lower. The interviewer's follow-up, why airlines have often earned poor returns, sits on the same logic: high fixed cost per flight and thin margins mean small swings in load factor or fuel swing profit hard.