Tips for IRR mental calculations and other interview maths questions

Would very much appreciate any tips/techniques to avoid sounding/looking like an idiot during an interview πŸ™

49 Comments
 

Thank you very much ! How this rule would apply for the following example:

-Purchase price/sale price: 100

-Cap rate: 5%

-LTV: 80% 

-Debt Cost: 5% per annum

No other costs

What would be the IRR after a 2 year holding period?

 

Thank you very much ! How this rule would apply for the following example:

-Purchase price/sale price: 100

-Cap rate: 5%

-LTV: 80% 

-Debt Cost: 5% per annum

No other costs

What would be the IRR after a 2 year holding period?

Interested in what kind of firm asked you this question?

As a side not have you ever tried modelling simple examples to try and understand how the maths works? I find that quite useful. Ie the coc here is 5% as debt is non accretive, so your irr will remain at 5% if there's no capital growth 

 

This is just a derivate of the rule of 72 - to 3x and to 4x takes 1.5 and 2 times longer than to 2x, respectively. Ergo, multiply 72 by 1.5 and 2.

To give you an example of how I personally approach it: if someone tells you a 3X was achieved in 5 years and asks you IRR. I know it doubled in ~3 years (5/1.5). 72/3 = 24% IRR. All rough math obviously but it's easy to remember and gets you close enough for a quick mental heuristic.

 
Funniest

Just build yourself a little table of 9 key numbers and use those as guard rails to get within 5% of whatever they throw at you

3yr  1.5x / 2x / 3x

5yr  1.5x / 2x / 3x

7yr 1.5x / 2x / 3x

Match IRRs up and should be able to navigate from there.  If they ever ask IRR on a 4x or 5x or something stupid just say "it don't matter baby we rollin' in carry at that point and beating off potential new LPs with a stick"

 
pudding

I’ve never been asked to calculate IRR in my head. That’s an absolutely ridiculous request and I doubt the interviewer can do it either…

Yup. If someone asked me to calculate an IRR in my head I'd be very confused about the interview and genuinely ask "why?" 

Seems like mental masturbation 

Commercial Real Estate Developer
 

Id maxime ex aperiam voluptas quia error quo. Omnis expedita molestias omnis magni. Non quos animi necessitatibus corporis. Et nemo et ipsum facere voluptates voluptatem. Ipsam sunt magni itaque reprehenderit provident incidunt. Sit tempore quis architecto voluptatem qui. Velit laborum fuga illo quibusdam libero ut.

Career Advancement Opportunities

October 2026 Investment Banking

  • Evercore 01 99.5%
  • Moelis & Company 01 99.0%
  • JPMorgan 01 98.4%
  • Guggenheim Partners 02 97.9%
  • Morgan Stanley 06 97.4%

Overall Employee Satisfaction

October 2026 Investment Banking

  • Moelis & Company No 99.5%
  • Morgan Stanley 02 99.0%
  • Evercore 01 98.4%
  • Banco Santander 02 97.9%
  • BMO Capital Markets 13 97.4%

Professional Growth Opportunities

October 2026 Investment Banking

  • Evercore 01 99.5%
  • Moelis & Company 01 99.0%
  • Morgan Stanley 05 98.4%
  • Goldman Sachs 01 97.9%
  • JPMorgan No 97.4%

Total Avg Compensation

October 2026 Investment Banking

  • Vice President (16) $429
  • Associates (57) $264
  • 3rd+ Year Analyst (8) $210
  • 2nd Year Analyst (28) $184
  • Intern/Summer Associate (16) $161
  • 1st Year Analyst (84) $151
  • Intern/Summer Analyst (76) $101
notes
16 IB Interviews Notes

β€œ... there’s no excuse to not take advantage of the resources out there available to you. Best value for your $ are the...”

Leaderboard

1
redever's picture
redever
99.2
2
BankonBanking's picture
BankonBanking
99.0
3
Secyh62's picture
Secyh62
99.0
4
kanon's picture
kanon
99.0
5
GameTheory's picture
GameTheory
98.9
6
dosk17's picture
dosk17
98.9
7
CompBanker's picture
CompBanker
98.9
8
Betsy Massar's picture
Betsy Massar
98.9
9
DrApeman's picture
DrApeman
98.9
10
bolo up's picture
bolo up
98.8
success
From 10 rejections to 1 dream investment banking internship

β€œ... I believe it was the single biggest reason why I ended up with an offer...”