Mental Math for Private Equity

By WSM Editorial|How is private equity mental math different from generic arithmetic?

"Private equity mental math focuses on leverage effects, return scenarios, and downside cases so you can triage deals before deep modeling starts."

— WSM Direct Answer

Why This Matters in Finance

PE teams evaluate many opportunities quickly. Fast arithmetic helps you pressure-test entry assumptions and identify whether a deal deserves full diligence resources.

Worked Examples

EXAMPLE 01

Entry equity check is $220M and exit equity is $385M over the hold period. MOIC?

▸ About 1.75x.

385 divided by 220 is roughly 1.75. That sets your first return anchor.

EXAMPLE 02

Debt is 5.0x EBITDA and EBITDA is $48M. Estimated debt at close?

▸ About $240M.

Multiply 48 by 5.0 for a quick debt estimate.

EXAMPLE 03

EBITDA margin rises from 18% to 21% on $600M revenue. Incremental EBITDA?

▸ About $18M.

Three-point margin increase on $600M gives 3% x 600M = $18M.

Check the annualized return

Use MOIC and holding period to check your return estimate. The calculator assumes one investment at entry and one receipt at exit, with no interim cash flows.

Check MOIC to annualized IRR →

Common Mistakes

✗Mixing enterprise and equity values in quick return math.

✗Ignoring leverage when interpreting operating improvements.

✗Treating a rough estimate as final when downside checks are missing.

Practice Questions

01.Equity entry is $300M and exit is $510M. Estimate MOIC.

02.Debt is 4.5x on $80M EBITDA. Approximate debt amount.

03.Margin improves 200 bps on $450M revenue. Incremental EBITDA?

04.Revenue falls 8% from $520M. New revenue estimate?

05.If EBITDA is $95M and EV multiple is 10x, what EV do you infer?

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How Wall St Math Helps

Wall St Math drills leverage-aware arithmetic so PE candidates can screen scenarios and discuss returns with confidence before model outputs are final.

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