Economic Capital
Economic capital is the cushion a bank estimates it actually needs to survive its own worst-case losses at a chosen confidence level — a firm's own risk-based number, distinct from the regulatory minimum it is legally required to hold.
Prerequisites: Value at Risk (VaR)
Regulators tell a bank the minimum capital it must hold. That number is a floor set by rules applying to every bank in the same category, not a measurement of any specific bank's actual risk. Economic capital is what a bank calculates for itself, internally, as the buffer it would truly need to absorb losses at some chosen confidence level without going insolvent — a bank's own answer to "how bad could a really bad year get, and do we have enough to survive it."
Economic capital is a self-assessed loss buffer, calibrated to the firm's actual risk exposures across every business line, rather than the standardized minimum imposed by a regulator. It is usually the larger of the two numbers.
The core calculation
At its simplest, economic capital is a Value-at-Risk-style calculation applied to the whole firm, at a very high confidence level chosen to match the bank's target credit rating:
In words: take the loss that would only be exceeded with probability (say, 99.9%, matching roughly a single-A credit rating's implied default probability), and subtract the expected change in value — because ordinary expected losses are supposed to be covered by pricing and reserves, and capital exists only for the unexpected part beyond that.
Worked example
A bank's credit portfolio has an expected annual loss of $50 million, already reflected in loan pricing and loss reserves. Modeling the full loss distribution, the bank finds that losses exceed $620 million only 0.1% of the time (the 99.9th percentile). Economic capital for this portfolio is:
That is, $620m − $50m = $570 million, which is what the bank needs held as a buffer, over and above pricing and reserves, to survive a loss this severe without the loss itself wiping out equity. If regulatory minimum capital for the same book, computed under standardized rules, comes to only $400 million, the bank holds to the higher internal number — because its own models say $400 million isn't actually enough.
What this means in practice
Economic capital feeds directly into how a bank allocates capital across business lines: a trading desk generating $10 million of profit on $50 million of economic capital is using capital more efficiently than one generating the same profit on $200 million, even if both comfortably clear the regulatory minimum. It also underlies risk-adjusted performance measures used to compare business lines that carry very different amounts of embedded risk.
Economic capital models are only as good as the loss distribution feeding them, and the tail — exactly the part that matters — is the hardest part of that distribution to estimate from limited historical data. A model calibrated on twenty years without a severe crisis will understate economic capital right up until the crisis it failed to anticipate arrives.
Practice in interviews
Further reading
- Jorion, Value at Risk (ch. 17, 'Economic Capital')