12 Technical-Round Mistakes IB Interviewers Report Most (and the Fixes)

Ask bankers who run interviews what sinks candidates in technical rounds, and the same themes come up again and again. It is rarely an obscure question nobody could answer. It is a familiar question handled badly: a memorized script that collapses under one follow-up, a sign error delivered with confidence, or a freeze where a bit of out-loud reasoning would have earned a pass.

Below are the twelve mistakes that come up most in these conversations, grouped into knowledge errors, process errors, and delivery errors — each with the fix. None of them require more raw intelligence; all of them require changing how you prep.

Knowledge mistakes (1-4)

These are the errors where the underlying understanding is missing, and no amount of polish covers for them.

• 1. Memorizing scripts without the mechanics underneath. The candidate recites a flawless DCF walkthrough, then cannot say why D&A gets added back. Fix: for every canned answer, prepare the two most likely follow-ups; if you cannot answer why for each step, you have not learned it yet.
• 2. Dropping the tax effect in change walkthroughs. Depreciation of 10 does not cut net income by 10; at a 40 percent tax rate it cuts net income by 6 because taxes fall by 4. Fix: always state your assumed tax rate out loud, then apply it — saying assuming a 40 percent tax rate buys you a beat to set up the math.
• 3. Getting working capital signs backwards. An increase in net working capital consumes cash; a decrease releases it. Receivables going up means cash you have not collected. Fix: anchor on one concrete example (receivables up = cash down) and derive the rest from it rather than memorizing a table.
• 4. Mixing enterprise value with equity metrics. Quoting EV over net income, or P/E on a firm-wide metric, signals the candidate does not know what a multiple measures. Fix: before quoting any multiple, ask whose claim the denominator represents — all capital providers pairs with EV, shareholders only pairs with equity value.

Process mistakes (5-8)

These candidates know the material but handle the calculation or the assumptions poorly in the moment.

• 5. Not stating assumptions. Answers that silently assume a tax rate, an interest convention, or flat working capital look lucky when right and careless when wrong. Fix: open quantitative answers with your assumptions — interviewers grade the habit itself.
• 6. Rushing arithmetic and skipping the sanity check. Dropping a zero on an EV calculation and not noticing is worse than being slow. Fix: after any computed number, check the magnitude against something you know — 100 of EBITDA at 10x must be 1,000, full stop.
• 7. Breaking the terminal value math. Choosing a perpetuity growth rate at or above WACC breaks the Gordon growth formula, and a growth rate far above long-run economic growth implies the company eventually outgrows the economy. Fix: keep g below WACC and around or below long-run GDP growth, and say why.
• 8. Mismatching cash flows and discount rates. Discounting unlevered free cash flow at the cost of equity, or levered cash flow at WACC, double-counts or drops the effect of debt. Fix: memorize the pairing — unlevered FCF with WACC gives enterprise value; levered FCF (or dividends) with cost of equity gives equity value.

Delivery mistakes (9-12)

The material is in the candidate's head, but the interview performance leaks value anyway. These are the most fixable of all.

• 9. Freezing on unfamiliar questions. Silence reads as absence of knowledge; visible reasoning reads as potential. Fix: have a stall-and-structure move ready — restate the question, name the closest concept you do know, and reason forward out loud from there.
• 10. Rambling past the answer. A two-minute answer to a thirty-second question buries the correct core and invites follow-ups on your weakest tangent. Fix: answer headline-first, then offer to go deeper — happy to walk through the mechanics if useful.
• 11. Arguing instead of taking the hint. When an interviewer says are you sure, they are usually offering a door, and doubling down on a wrong answer closes it. Fix: treat pushback as data — re-derive the step out loud rather than defending the conclusion.
• 12. Not knowing your own resume cold. Claiming a DCF on your resume and then fumbling which discount rate you used is reported constantly, and it damages trust more than a missed question. Fix: for every technical claim on your resume, prepare the same follow-up depth you would for a core question.

The pattern behind all twelve

Notice what these have in common: almost none of them are about missing knowledge of rare topics. They are about shallow encoding (memorizing without mechanics), missing habits (assumptions, sanity checks), and untested delivery (first out-loud rep happening in the real interview).

That maps to a clear prep prescription. Learn in dependency order so mechanics support the scripts. Drill by answering out loud, not rereading, so the delivery rep count is high before it matters. And log every miss, because your personal top-three mistakes from this list are far more predictive than the average candidate's.

How to inoculate yourself before the real thing

You cannot fix delivery mistakes by reading about them, including here. Each of these needs a live rep where the mistake can actually happen and get corrected.

1. 01Do at least two mock interviews with someone who will interrupt and push back, not a friend who nods
2. 02Practice one deliberately unfamiliar question per session to train the stall-and-structure move
3. 03Record one mock and count your rambles — answers that keep going after the question is answered
4. 04Run daily mixed-topic recall (the Daily 10 works well here) so old mechanics stay sharp under new topics
5. 05Write out follow-ups for every line on your resume and drill them like core technicals

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