Reserve Ratio Calculator

The Reserve Ratio Calculator measures how much of a bank’s deposits are held as reserves, how much remains as loanable funds, and what simple money multiplier follows from that reserve ratio. It is useful for macroeconomics homework, banking examples, and quick checks of fractional-reserve logic. The calculation is intentionally mechanical: deposits and reserves go in, and the reserve ratio, loanable funds, loanable share, and simple multiplier come out.

This page is about bank balance-sheet ratios, not household savings. If you are planning personal cash reserves, use the budget calculator or savings goal calculator. If you are studying how interest accumulates on a bank account, use the interest calculator. For the closely related textbook multiplier formula by itself, see the money multiplier calculator.

What the reserve ratio means

A bank reserve is money held in cash, vault cash, or balances at the central bank rather than lent out. Deposits are the customer or system-wide deposit liabilities being supported by those reserves. The reserve ratio compares the two. If a bank has one hundred million dollars of reserves and one billion dollars of deposits, reserves equal 10% of deposits.

That ratio can be interpreted in two ways. First, it shows liquidity held against deposits. Second, in a simplified fractional-reserve model, it determines the maximum deposit expansion implied by a fixed reserve base. A lower reserve ratio produces a larger simple money multiplier, while a higher reserve ratio produces a smaller one. Real banking systems are more complicated, but the ratio remains a basic way to connect reserves, deposits, and lending capacity. It also gives students a clean bridge between an individual bank balance sheet and the aggregate money-supply examples used in macroeconomics courses.

Formula used by this calculator

The reserve ratio is:

$\text{reserve ratio} = \frac{\text{reserves}}{\text{deposits}} \times 100\%$

Loanable funds are the part of deposits not held as reserves:

$\text{loanable funds} = \text{deposits} - \text{reserves}$

The loanable share is:

$\text{loanable share} = \frac{\text{loanable funds}}{\text{deposits}} \times 100\%$

The simple money multiplier is deposits divided by reserves, which is the same as one divided by the reserve ratio expressed as a decimal:

$\text{simple money multiplier} = \frac{\text{deposits}}{\text{reserves}}$

The form requires deposits greater than zero, reserves at least zero, and reserves no greater than deposits. If reserves are zero, the ratio is 0% and loanable funds equal deposits; the calculator omits the multiplier because it would be infinite.

Worked example

Use the default inputs: deposits of 1,000,000,000 dollars and reserves of 100,000,000 dollars. The reserve ratio is:

$\frac{100{,}000{,}000}{1{,}000{,}000{,}000} \times 100\% = 10\%$

The primary result is therefore 10%, labeled as reserves as a share of deposits. Loanable funds are:

$1{,}000{,}000{,}000 - 100{,}000{,}000 = 900{,}000{,}000$

The loanable share is:

$\frac{900{,}000{,}000}{1{,}000{,}000{,}000} \times 100\% = 90\%$

The simple money multiplier is:

$\frac{1{,}000{,}000{,}000}{100{,}000{,}000} = 10$

So the calculator reports 100,000,000 dollars in reserves held, 900,000,000 dollars in loanable funds, a 90% loanable share, and a 10x simple money multiplier. The copy text summarizes the same reserve ratio, reserves, deposits, and loanable funds.

How to use the result

For a single bank, the reserve ratio is a snapshot of how much deposit funding is being kept highly liquid. A higher actual reserve ratio may reflect caution, weak loan demand, liquidity management, or a regulatory environment that encourages extra reserves. A lower actual reserve ratio may reflect more aggressive lending or a different balance-sheet strategy.

For a banking system example, the simple money multiplier shows the maximum deposit expansion in a very simplified model. If the reserve ratio is 10%, a one-dollar reserve base can support up to ten dollars of deposits in the model. If the reserve ratio is 20%, the multiplier falls to five. OpenStax uses this logic to explain how banks create money through repeated deposit and lending rounds.

Limitations and common mistakes

Do not confuse actual reserve ratio with required reserve ratio. The Federal Reserve’s reserve requirement rules are regulatory settings; the calculator simply measures the numbers you enter. Also do not treat the simple money multiplier as a forecast. Modern banking depends on capital requirements, liquidity rules, interest paid on reserves, credit demand, loan standards, and central-bank operations. A bank cannot create loans just because a formula says a multiplier is large.

Make sure deposits and reserves are measured on the same basis. If deposits are in millions, reserves must also be in millions. If deposits are system-wide, reserves should be system-wide. Avoid entering required reserves in one field and actual deposits from a different date or institution in the other.

Formula sources and scope

• Principles of Economics 3e — OpenStax, Rice University (peer-reviewed open textbook); 2022 third edition, ISBN 978-1-951693-60-2; Jurisdiction-neutral economics definitions. Supports: reserveRatio=reserves/deposits×100; money multiplier 1/ratio is only a simplified textbook identity, not a current policy prediction. Accessed 2026-07-09.
• Reserve Requirements — Board of Governors of the Federal Reserve System; effective reserve requirement table; accessed 2026-07-09; United States. Supports: reserveRatio=reserves/deposits×100; money multiplier 1/ratio is only a simplified textbook identity, not a current policy prediction. Accessed 2026-07-09.
• Principles of Finance — OpenStax, Rice University (peer-reviewed open textbook); 2022 first edition, ISBN 978-1-951693-54-1; Jurisdiction-neutral finance definitions. Supports: reserveRatio=reserves/deposits×100; money multiplier 1/ratio is only a simplified textbook identity, not a current policy prediction. Accessed 2026-07-09.

These sources support the stated formula or definition. Results remain estimates based on the entered values and do not replace financial, legal, tax, lending, or investment advice. Compare periods, units, accounting definitions, and jurisdiction-specific rules before acting.

Sources

• Federal Reserve, Reserve Requirements — policy background on reserve requirement rules.
• OpenStax, How Banks Create Money — textbook explanation of reserves, deposits, and the money multiplier.
• OpenStax, How a Central Bank Executes Monetary Policy — central-bank context for reserve requirements and monetary policy.