IRR vs MOIC: The Difference, Plus the Mental Shortcuts That Make Paper LBOs Easy (2x in 5 Years ≈ 15%)

If an interviewer asks "What's the IRR on a 2x over five years?", the answer you want is "about 15%", delivered in under three seconds. No calculator, no long pause, no visible math.

This post covers two things. First, what IRR and MOIC actually measure and why they can tell different stories. Second, the mental shortcuts that let you convert between them in your head, which is exactly what you'll need in a paper LBO or a "walk me through a deal" question.

The Quick Definitions

MOIC: How Much Money Did You Make?

MOIC (Multiple on Invested Capital) is simple: total cash you got back divided by total cash you put in.

• Invest $100M, get back $250M → 2.5x MOIC
• Invest $100M, get back $100M → 1.0x (you got your money back, nothing more)

MOIC answers "how much?" It says nothing about "how fast?"

IRR: How Fast Did You Make It?

IRR (Internal Rate of Return) is the annualized return that makes the net present value of all your cash flows equal zero. In plain English: it's your compound annual growth rate, adjusted for the timing of every dollar in and out.

When there's just one cash flow in and one cash flow out, the math simplifies nicely:

IRR = MOIC^(1 / years) − 1

So for a 2x over 5 years: 2^(1/5) − 1 = 1.149 − 1 ≈ 14.9%. That's where the famous "2x in 5 years ≈ 15%" comes from.

Why You Need Both

Here's the core idea: MOIC ignores time, and IRR ignores size. Each metric covers the other's blind spot.

Look at these two deals:

• Deal A: 3.0x over 7 years → about 17% IRR
• Deal B: 2.0x over 3 years → about 26% IRR

Deal B has the better IRR. Deal A made more money per dollar invested. Which is "better"? It depends on what the investor cares about, and that's precisely the kind of nuance interviewers want to hear you discuss.

When IRR Looks Great but Isn't

A high IRR on a quick flip can look amazing while producing very little actual profit. Earn a 1.2x in six months and your IRR is about 44%. Sounds incredible, but you only made 20 cents on the dollar, and now you need to find somewhere else to put that money to work.

This is why many limited partners like to say "you can't eat IRR." At the end of the day, they want real cash multiples.

When MOIC Looks Great but Isn't

A 3.0x sounds strong until you learn it took 12 years. That works out to roughly a 9.6% IRR, which is not much more than many investors might expect from far more liquid, lower-risk options. A big multiple stretched over a long hold can be pretty mediocre.

How Timing of Cash Flows Moves IRR (But Not MOIC)

This is a favorite interview concept, so let's run the numbers.

Two deals, both 2.0x MOIC, both 5 years:

• Deal 1: Invest $100, receive $200 at exit in year 5
• Deal 2: Invest $100, receive a $50 dividend recap in year 2, then $150 at exit in year 5

Total cash back is $200 in both cases, so MOIC is identical at 2.0x. But the IRRs differ:

• Deal 1: ≈ 14.9%
• Deal 2: ≈ 18.4%

Getting money back earlier boosts IRR, because that cash spent less time "at work." This is why dividend recaps and early partial exits are common levers for improving IRR. In an interview, if someone asks "how can a sponsor increase IRR without changing the exit value?", earlier distributions is a great answer.

The Mental Shortcuts

Now the fun part. In a paper LBO, you'll usually compute MOIC easily (exit equity ÷ entry equity) and then need to estimate IRR quickly. Here's how.

Shortcut 1: Memorize a Few Anchor Points

You don't need a hundred numbers. A handful of anchors gets you through almost every interview:

• 2x in 3 years ≈ 26%
• 2x in 5 years ≈ 15%
• 2.5x in 5 years ≈ 20%
• 3x in 5 years ≈ 25%

Notice the pattern for 5-year holds: every extra 0.5x adds roughly 5 points of IRR in the 2x to 3x range. That one observation covers a huge share of paper LBO answers, since 5 years is the default hold period in most case prompts.

Shortcut 2: The Cheat Sheet Table

Here's a broader grid, rounded to the nearest percent:

Two things worth noticing:

• The same multiple gets much less impressive with time. A 2x drops from 26% to 10% just by stretching from 3 to 7 years.
• IRR is not linear in MOIC. Going from 1.5x to 3.0x over 5 years is doubling the multiple, but IRR roughly triples (8% to 25%), because you're dealing with exponents.

Shortcut 3: The Rule of 72 (Think in Doublings)

The Rule of 72 says the number of years to double your money ≈ 72 ÷ annual return. Flip it around:

IRR to double ≈ 72 ÷ years to double

• Double in 5 years → 72 ÷ 5 ≈ 14.4% (actual: 14.9%)
• Double in 6 years → 72 ÷ 6 = 12% (actual: 12.2%)
• Double in 3 years → 72 ÷ 3 = 24% (actual: 26%)

It works best for moderate returns. At higher returns it underestimates, so nudge your answer up a couple of points once you're above roughly 20%.

You can also chain doublings. A 4x is just two doublings:

• 4x in 6 years = 2x every 3 years → about 26% (this one is exact, since 4^(1/6) equals 2^(1/3))
• 4x in 5 years = 2x every 2.5 years → rule of 72 says about 29%, actual is about 32%

Shortcut 4: Interpolate Between Anchors

Got a 2.2x over 5 years? It sits between 2.0x (15%) and 2.5x (20%), about 40% of the way along. Estimate around 17%. The precise answer is about 17.1%.

Interviewers aren't looking for decimal-point accuracy here. They want to see you anchor, adjust, and land within a point or two.

Putting It Together: A Mini Paper LBO

Let's say the prompt goes like this:

• A sponsor buys a company for $500M, funded with $200M of equity and $300M of debt
• After 5 years, the company sells for $700M
• Remaining debt at exit is $200M

Step 1: Exit equity. $700M − $200M = $500M

Step 2: MOIC. $500M ÷ $200M = 2.5x

Step 3: IRR. 2.5x over 5 years → your anchor says about 20%

Done. You just answered a paper LBO without touching a calculator, and you can spend the rest of your time talking through the value creation (debt paydown, EBITDA growth, multiple expansion), which is where you actually impress people.

How to Talk About This in an Interview

A few tips for sounding sharp:

• State both metrics. "That's a 2.5x MOIC, so roughly a 20% IRR over five years." This shows you know they measure different things.
• Say "roughly" or "about." It signals you're using a shortcut on purpose, not guessing.
• Mention the tradeoff if it's relevant. If a deal has a high IRR but low multiple, point out that it may have been a quick win with limited absolute profit.
• Know the formula caveat. The MOIC^(1/n) − 1 shortcut only works with one cash flow in and one out. If there are dividends or follow-on investments, you need the full IRR calculation, and you should say so.

The Bottom Line

MOIC tells you how much you made. IRR tells you how fast. Good investors and good interview candidates always think about both.

For the mental math, lock in four anchors (2x/3y ≈ 26%, 2x/5y ≈ 15%, 2.5x/5y ≈ 20%, 3x/5y ≈ 25%), keep the Rule of 72 in your back pocket, and interpolate for everything in between. Practice converting a few random multiples a day, and by interview season it'll feel automatic.