Put Jamie Dimon's rule through your numbers

One rule JMM has located in a dated source, rebuilt as a working calculator, and taken a position on.

Sources located: JPMorganChase
Source years: 2026
JMM verdicts: holds up

Portrait: Lauren Hurley / No 10 Downing Street, Open Government Licence v3.0, via Wikimedia Commons. Self-hosted by JMM.

Fortress balance sheet model

What does fortress capital do to return on equity?

holds up Carrying surplus capital costs return every year and pays for itself once a decade. That trade has been settled by events. JPMorganChase, 2026Open model

Read the source before the output

Every rule here is located in a dated JPMorganChase document, the passage is quoted, and the calculator implements what that passage says rather than a rounded version of it. Where JMM agrees with a rule, the page says so and explains what the rule is buying you.

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.