What it means
A bank takes in deposits and lends most of the money out, which means it cannot pay everyone at once. To meet daily withdrawals and payments, it keeps a portion in forms that are available immediately.
These holdings are the primary reserves. The reserves are held as cash and as balances at the central bank.
They earn little or no interest, so banks try to hold enough for safety without holding so much that profit suffers. This is a basic trade-off between safety and return.
Some countries set minimum reserve requirements as a percentage of deposits, and the percentage is determined by the central bank and may change over time. Others rely on liquidity rules that focus on holding high-quality liquid assets rather than a fixed reserve ratio.
Either way, the aim is to ensure the bank can meet its obligations when customers ask for their money. Secondary reserves are a second layer, made up of short-term securities such as government bills that can be sold quickly at a predictable price.
They earn some interest and can be converted to cash within a short time. A bank typically uses its primary reserves first and its secondary reserves when needs are larger.
For non-bankers the idea is useful because it explains why banks fail when depositors lose confidence. Even a sound bank cannot repay all its deposits at once, so a sudden rush of withdrawals can exhaust its primary reserves.
That risk is the reason central banks stand ready to lend in a crisis and deposit insurance exists. Some countries define reserves slightly differently, so the details depend on local banking rules.
In practice the principle is the same everywhere: the most liquid assets sit at the front of the line for meeting cash demands.
In practice
Real-world examples.
Example
A community bank stocks extra cash before a holiday weekend, when customers withdraw more. Its treasurer tracks vault cash daily to make sure primary reserves cover the expected demand. Extra cash is ordered from the central bank or a cash handling firm in advance.
Example
A regional bank suffers rumours on social media and sees heavy withdrawals within a day. It uses its balances at the central bank to pay customers while it arranges short-term funding. The central bank balance is the first line of defence.
Example
A chief financial officer of a bank compares the cost of holding idle reserves with the risk of a shortfall. She sets an internal minimum that sits comfortably above the regulatory floor. The cost of holding reserves is measured as the interest the bank gives up.
Formula
Calculation
Primary reserve ratio = (Cash in vault + Balances at the central bank) / Total deposits.
A bank holds $50,000,000 in cash in its vaults and branches and $150,000,000 in balances at the central bank. Primary reserves are $50,000,000 + $150,000,000 = $200,000,000. Its customers have deposited $2,000,000,000.
The primary reserve ratio is $200,000,000 / $2,000,000,000 = 0.10, or 10%. If depositors withdraw $300,000,000 in a week, the bank can meet the first $200,000,000 from primary reserves and must then sell secondary reserve securities or borrow to cover the remaining $100,000,000.Case study
Seen in the real world.
Eastgate Savings is a fictional bank that grew quickly by offering high deposit rates. Its lending expanded faster than its deposit base, and its primary reserves fell from 12% to 6% of deposits in an illustrative two-year period.
Then a competitor failed, and customers across the region withdrew money out of caution. Eastgate's reserves lasted only two days, and the board had to borrow urgently at a high cost to meet the demand.
The fictional bank survived but the episode led to a policy of holding a larger buffer and diversifying funding. The story shows why primary reserves are a safety measure and not an idle waste of money. The treasurer began reporting the reserve ratio to the board every week.
Watch out
Common mistakes.
- Treating primary reserves as profit-earning assets, when they earn little or nothing by design. Their return is safety, not interest.
- Assuming a bank holds enough cash to repay all depositors at once, when banks rely on only a fraction. This is why confidence matters so much in banking.
- Confusing primary reserves with capital, which is the bank's own funding and absorbs losses. Capital is a separate buffer on the other side of the balance sheet.
Questions
People also ask.
What is the difference between primary and secondary reserves?
Primary reserves are cash and central bank balances, while secondary reserves are short-term securities that can be sold quickly. Secondary reserves earn interest but take longer to turn into cash.
Who sets the minimum reserve?
The central bank or banking regulator does so in many countries, and the requirement can change over time.
Why do banks not hold more reserves?
Reserves earn little, so holding too many reduces the bank's profit. Regulators therefore set minimum levels to protect depositors.
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