Higher interest rates are often good for bank earnings. Loans and other interest-earning assets can generate more income, especially when they reprice faster than deposits and other funding sources.
But there is another side to the story. Higher market yields reduce the value of older fixed-rate bonds. Deposit costs may eventually rise. Borrowers may struggle to repay. A bank can therefore report stronger income while important risks are building elsewhere on its balance sheet.
A profitable bank is not automatically a low-risk bank. The quality, durability and risks behind the profit matter.
What the Bank of Japan found
On 4 September 2026, the Bank of Japan published its review of Japanese banks’ financial results for the 2025 fiscal year.
Net income increased at Japan’s major financial groups and regional banks, although it declined at shinkin banks, which are cooperative regional financial institutions. Core pre-provision profitability improved across all bank categories, largely because rising yen interest rates strengthened net interest income.
At the same time, losses from bond sales placed downward pressure on earnings. The Bank of Japan linked these losses to rising yen interest rates. Capital ratios remained comfortably above regulatory requirements, although they declined somewhat at internationally active banks. The Bank of Japan’s full assessment is available here.
This was not a new interest-rate decision. It was evidence of how earlier rate increases were already moving through bank income statements and balance sheets.
Why bond prices fall when interest rates rise
Consider a bank that buys a ten-year government bond paying 3% a year. If newly issued bonds later offer 5%, an investor will not normally pay the original price for the older 3% bond. Its market price must fall until its effective return becomes competitive with the new market rate.
The longer the remaining life of the bond, the more sensitive its price will usually be to a change in interest rates. This sensitivity is commonly described as duration risk.
If the bank can hold the bond until maturity and the issuer pays as agreed, the bank may continue collecting the contractual interest and principal. But the lower market value is still economically important.
It becomes especially important when the bank needs to sell the bond to meet deposit withdrawals, raise liquidity, reduce risk or reposition its portfolio. At that point, a valuation decline can become a realized loss.
Why stronger bank income can hide growing risk
The first effect of higher rates may look positive. Loans reprice, yields on new securities increase and net interest income improves. But four risks can develop underneath the stronger headline result.
- Bond valuation risk: older fixed-rate securities lose market value as yields rise.
- Liquidity risk: the bank may need to sell those securities at a loss when cash is required.
- Funding risk: depositors eventually demand higher returns, reducing the initial improvement in the bank’s interest margin.
- Credit risk: borrowers facing more expensive loans may experience weaker cash flow and higher repayment pressure.
The sequence matters. Asset yields may rise before deposit costs fully adjust, producing an early increase in profit. Later, funding costs and credit losses can catch up.
This is why boards should not assess a high-rate environment using net interest margin alone.
The accounting result may not show the full economic exposure
The effect on reported profit depends partly on how a security is classified and whether it is sold. Some fair-value movements pass through profit or loss. Others may be recorded in other comprehensive income, while securities measured at amortized cost may not show the same immediate market-price movement in reported earnings.
That accounting treatment does not make the economic risk disappear.
A board still needs to understand the current market value, remaining duration, funding source and likelihood that an asset may need to be sold. A position that looks stable under normal conditions can become a problem during a liquidity shock.
The lesson for Nigerian banks
Nigeria’s interest-rate environment is much tighter than Japan’s, but the underlying balance-sheet mechanics are similar. At its May 2026 meeting, the Central Bank of Nigeria retained the monetary policy rate at 26.5% and the cash reserve requirement for deposit money banks at 45%. The CBN publishes its current and previous monetary policy decisions here.
Nigerian banks hold Treasury bills, Federal Government bonds and other fixed-income securities. High yields can produce substantial income. They can also make government securities attractive relative to lending to a manufacturer or growing business that carries higher credit, monitoring and capital costs.
This creates two different questions for bank boards:
- Is the bank earning more because its underlying customer franchise and lending business are improving?
- Or is a large part of the improvement coming from a high-rate environment that may also be increasing duration, liquidity and concentration risks?
Private-sector credit continues to grow in nominal terms, according to the CBN’s money and credit statistics. But the more important test is whether productive businesses can obtain credit at a price and tenor that their cash flows can support. The CBN’s money and credit data can be viewed here.
A banking system can be profitable and liquid, yet still provide too little patient and affordable capital to the productive economy.
What bank boards should ask
Credit risk remains essential, but it should not crowd out interest-rate risk in the banking book. Boards need a clear view of what could happen if the yield curve moves again.
The discussion should cover:
- the duration and maturity profile of the securities portfolio;
- unrealized gains and losses by accounting category;
- the effect of 100, 200 and 300-basis-point rate movements;
- both parallel and uneven changes across the yield curve;
- securities that might need to be sold during a liquidity stress;
- the speed at which deposits and wholesale funding will reprice;
- the effect of higher loan rates on defaults and restructurings;
- capital adequacy after valuation and credit losses; and
- concentration in government securities, sectors and funding sources.
The aim is not to avoid all interest-rate exposure. Banking depends on taking and managing risk. The aim is to know where the risk sits, how large it is and what management will do if conditions move against the bank.
What investors should look for beyond profit
Investors should separate reported earnings from sustainable earnings.
A strong profit figure deserves further questions:
- How much of the increase came from net interest income?
- How much depended on government-security yields?
- How much was supported by foreign exchange revaluation or other non-recurring items?
- What happened to the cost of deposits?
- Are impaired loans and restructurings beginning to rise?
- What valuation losses sit outside the headline profit figure?
- How much capital would remain under a combined interest-rate, liquidity and credit shock?
The better investment question is not only how much profit the bank made. It is how repeatable the profit is and how much risk the bank carried to produce it.
Why this matters to manufacturers and growing businesses
For businesses, the issue appears in the availability and price of credit.
When government securities offer attractive risk-adjusted returns, banks may have less incentive to provide long-term funding to manufacturers, exporters, infrastructure providers and smaller businesses. These companies may require deeper credit assessment, closer monitoring, collateral management and longer repayment periods.
The result can be a difficult combination: strong bank earnings, high sovereign borrowing and inadequate affordable financing for the businesses expected to create jobs and expand production.
Companies should therefore avoid depending on one form of bank debt. Depending on the project, they may need to combine retained earnings, customer advances, supplier credit, asset finance, private capital, development-finance funding and appropriately structured local or foreign-currency debt.
The global capital-flow effect
Japan holds one of the world’s largest pools of institutional savings. For many years, very low domestic yields encouraged Japanese investors to seek better returns overseas.
As Japanese yields become more attractive, some investors may keep more capital at home or require higher returns before investing abroad. This does not mean Japanese capital will suddenly leave Africa. It does mean African sovereigns and companies may face greater competition for global savings.
High nominal yields alone will not be enough. Countries and companies will need credible policies, stronger foreign exchange stability, transparent reporting, reliable governance and investment structures that allow capital to enter and exit with confidence.
The executive conclusion
Japan’s experience shows why rising interest rates must be assessed across the whole balance sheet.
Higher rates can strengthen asset yields and net interest income. At the same time, they can reduce bond values, increase funding costs, weaken borrowers and create liquidity pressure.
For Nigerian and African bank boards, stronger profit should not reduce attention to duration, valuation losses, deposit repricing, liquidity and credit quality.
For businesses, high bank profitability should not be mistaken for an automatic increase in affordable credit.
For investors, the decisive question is not simply, “How much profit did the bank make?”
How sustainable is the profit, and how much risk did the bank take or continue to carry to produce it?