Put Warren Buffett's rules through your numbers
Four rules JMM has located in a dated source, rebuilt as a working calculator, and taken a position on. One outside party has published a figure on them, and that number is on the page next to the rule.
- Sources located
- Berkshire Hathaway
- Source years
- 1987 to 2017
- JMM verdicts
- holds up, depends on you
90/10 portfolio model
How would a 90/10 split allocate and grow your money?
holds up Tested over 86 retirements and it survived 97.7% of them. The catch is who it was written for. Berkshire Hathaway, 2014Open model
Investment fee-drag calculator
How much ending wealth can a fee difference consume?
holds up The most reliably correct piece of advice on this site. Fees are the one variable you control. Berkshire Hathaway, 2017Open model
Owner earnings calculator
What cash can a business distribute without weakening its position?
depends on you The right question, built on a number no outsider can actually observe. Berkshire Hathaway, 1987Open model
Five-year earnings range test
Is the lower end of your five-year earnings range reasonable at today’s price?
depends on you A filter, not a valuation. Its real value is telling you when to walk away. Berkshire Hathaway, 2014Open modelNot every rule here survives its own arithmetic
JMM does not grade these rules as a set. Two of them carry a verdict other than "holds up", and the page says why in JMM's own words rather than leaving the evidence to speak for itself.
Each page separates three things people usually run together: what the source states, what JMM's model adds to make it computable, and where the rule itself breaks. The last one is not the calculator's limitations list. It is the failure of the idea, which is the part the person who published the rule has no reason to write down.