Cost of Funds Calculator

What the Cost of Funds Number Represents

Cost of funds is the blended interest rate an institution pays for the money it lends out and invests. Banks, credit unions, and non-bank lenders report it as interest expense divided by average funding balances, usually annualized so periods of different lengths can be compared. The figure answers one question: for every dollar of deposits and borrowings on the books, how many cents per year go out the door as interest?

Cost of funds = annual interest expense / average total funds x 100

The rate is the denominator side of the oldest business in banking, which buys money at one rate and sells it at another. Deposit pricing desks use it to decide what they can pay on a new 12 month certificate; loan pricing teams use it as the floor beneath any commercial quote. Regulators track it too: the FFIEC Uniform Bank Performance Report publishes cost-of-funds and net interest margin ratios for every insured institution, which makes peer comparison straightforward.

Note the denominator choice. Some analysts divide by total liabilities, others by interest-bearing liabilities only, and a few use average earning assets. Each produces a different number from the same expense. Pick one definition, state it, and keep it constant, because a cost of funds that silently changes denominator mid-year is worse than no metric at all.

Weighted Average Cost Across Funding Sources

No institution pays a single rate. Demand deposits pay almost nothing, savings accounts pay a little, certificates pay market rates, and wholesale borrowings pay the most. The blended cost is a balance-weighted average:

Weighted cost = (B1 x r1 + B2 x r2 + ... + Bn x rn) / (B1 + B2 + ... + Bn)

A $250 million funding book shows how the mix drives the result. Checking anchors the low end, certificates dominate the balance sheet, and a small wholesale line carries the highest rate.

Two structural facts follow. First, the rates that look expensive are not always the ones that cost the most: certificates at 4.35 percent carry 32 percent of the balances and 45 percent of the expense. Second, a shift in mix moves the blended rate without any change in posted rates. Moving $10 million from savings at 2.10 percent into certificates at 4.35 percent adds $225,000 of annual expense and lifts the blended cost of funds to 3.154 percent.

Annualizing Monthly and Quarterly Interest Expense

Interest expense arrives monthly on the general ledger while the metric is quoted annually. Multiply the period expense by the number of periods in a year, then divide by average balances for that same period. Using average balances rather than end-of-period balances matters: a deposit surge in the final week of a month would otherwise make the rate look artificially cheap.

Annualizing a single month amplifies noise. A month with 31 days carries roughly 3 percent more interest than a 30 day month at the same rate, and a month with a large certificate maturity can swing the average balance by several percent. Most treasury teams annualize the year-to-date figure instead: total expense for the year so far, multiplied by 12 divided by the number of months elapsed, over the year-to-date average balance.

Spread, Net Interest Margin, and Non-Earning Assets

Cost of funds only becomes useful next to the yield earned on the other side of the balance sheet. The difference is the funding spread, quoted in basis points (one basis point is 0.01 percentage point):

Spread = earning-asset yield - cost of funds

Net interest margin is a different ratio, and confusing the two overstates performance. Margin divides net interest income by average earning assets, not by total funds:

Net interest margin = (interest income - interest expense) / average earning assets

In the $250 million example, earning assets total $230 million at a 6.10 percent yield. Interest income is $14,030,000, net interest income is $6,370,000, and margin is 2.77 percent. The spread was 3.036 percent, so $20 million of cash, premises, and other non-earning assets consume most of the gap. That dilution is normal and worth tracking separately, because a bank can hold a healthy spread and still post a thin margin.

Step-by-Step Worked Examples

Example 1: Community bank deposit book

A community bank holds $40 million in checking at 0.75 percent, $60 million in savings at 2.10 percent, $80 million in certificates at 4.35 percent, $50 million in money market accounts at 3.20 percent, and $20 million of wholesale borrowings at 5.10 percent.

1. Checking expense: $40,000,000 x 0.0075 = $300,000.
2. Savings expense: $60,000,000 x 0.0210 = $1,260,000.
3. Certificate expense: $80,000,000 x 0.0435 = $3,480,000.
4. Money market expense: $50,000,000 x 0.0320 = $1,600,000.
5. Wholesale expense: $20,000,000 x 0.0510 = $1,020,000.
6. Total expense: $300,000 + $1,260,000 + $3,480,000 + $1,600,000 + $1,020,000 = $7,660,000.
7. Total funds: $40,000,000 + $60,000,000 + $80,000,000 + $50,000,000 + $20,000,000 = $250,000,000.
8. Cost of funds: $7,660,000 / $250,000,000 = 3.064%.
9. Spread against a 6.10 percent asset yield: 6.10% - 3.064% = 3.036%, or 303.6 basis points.

Example 2: Blended borrowing cost for a small business

A manufacturer funds working capital with a $200,000 line of credit at 6.50 percent, a $500,000 equipment term loan at 7.20 percent, and a $300,000 owner note at 4.00 percent.

1. Line of credit: $200,000 x 0.0650 = $13,000.
2. Term loan: $500,000 x 0.0720 = $36,000.
3. Owner note: $300,000 x 0.0400 = $12,000.
4. Total interest: $13,000 + $36,000 + $12,000 = $61,000.
5. Total debt: $200,000 + $500,000 + $300,000 = $1,000,000.
6. Blended cost of funds: $61,000 / $1,000,000 = 6.10%.

The same arithmetic applies to any borrower weighing a refinance: replacing the term loan with a 6.40 percent facility would cut annual interest to $32,000 and pull the blended rate down to 5.70 percent.

What Moves the Number Up or Down

Four forces dominate quarter-to-quarter movement in cost of funds:

• The policy rate. Deposit and wholesale rates reprice with the fed funds target range. The Federal Reserve H.15 release tracks the benchmark series that most floating-rate funding follows.
• Deposit mix. Growth in certificates and money market accounts raises the blended rate even when posted rates stand still, because those products carry the highest rates on the book.
• Certificate ladder repricing. Certificates issued during a high-rate period keep paying that rate until maturity. A ladder priced at 4.35 percent when the market was higher still costs 4.35 percent after rates fall, which holds the blended rate above the current offering rate for a year or more.
• Wholesale reliance. Brokered deposits and Federal Home Loan Bank advances price at market and are the first line to rise when liquidity tightens. National deposit rate ceilings and weekly rate caps are published by the FDIC, and any institution paying above those levels is buying funds at a premium.

Using Cost of Funds in Pricing and Liquidity Decisions

Three routine decisions depend on the number. Loan pricing starts here: a commercial quote must clear the marginal cost of the funding that will support it, not the historical average, because new loans are funded with new money. A 6.10 percent asset yield on a book funded at 3.064 percent looks generous, but if the next dollar of funding costs 4.35 percent, that is the floor for the next loan.

Product pricing on the deposit side works the same way in reverse. Raising a savings rate by 50 basis points on $60 million adds $300,000 of annual expense and pushes the blended cost to 3.184 percent; the branch has to originate roughly $4.9 million of additional 6.10 percent loans just to break even on that repricing.

Liquidity planning adds a stress view. Institutions typically recompute cost of funds under a scenario where rate-sensitive deposits leave and are replaced by wholesale borrowings 150 to 200 basis points higher. That stressed rate, not the current one, is what belongs in contingency funding plans. Recompute the metric monthly, reconcile it against the general ledger interest accounts each quarter, and keep the definition stable so the trend line means something.