Bank Reserve Ratio and Money Multiplier Calculator

In the textbook fractional-reserve model, banks hold a fraction of deposits as reserves and lend the rest. The reserve ratio is that fraction, and the simple money multiplier is its reciprocal: if the ratio is 10%, the multiplier is 10, meaning $1 of reserves could support $10 of deposits if every bank were fully loaned up. Real banking is richer than that identity—excess reserves, capital rules, and central-bank facilities all intervene—but the ratio is still the starting map. The reserve ratio calculator treats the required-reserves field as the reserve balance you are measuring against deposits. Actual reserve ratio = required reserves / total deposits. Theoretical money multiplier = 1 / actual reserve ratio. Total reserves = required reserves + excess reserves. If you enter a stated reserve requirement percentage, it is shown beside the actual ratio so you can see a surplus or shortfall; it does not replace the actual ratio in the multiplier. Students use the multiplier when working through deposit-expansion examples in a principles-of-banking course. Analysts use the actual ratio when a bank’s reserve report is compared with a stated policy or internal target rate. After many central banks moved to ample reserves and a 0% required-reserve ratio, the textbook multiplier is a teaching device more than a forecast of broad money. Entering a very small required-reserve balance produces a very large multiplier; that is algebra, not a prediction of lending. The identity ignores currency drain, capital constraints, and banks’ willingness to lend. Excess reserves can sit idle, which is why the simple multiplier is a ceiling rather than a forecast of broad money. Use published reserve and deposit figures for a real institution, keep deposits and reserves in the same currency and reporting date, and do not treat a classroom 10× example as a lending or monetary-policy plan.