Blog · Finance metrics and formulas · Banking
The cost income ratio compares bank operating expenses with operating revenue. Define the inclusions, calculate a worked example by business unit, and reconcile changes before interpreting efficiency.
The cost income ratio measures how much bank operating revenue is absorbed by operating expense. For the unadjusted internal definition used here, divide noninterest expense by net interest income plus noninterest income. A lower percentage means fewer expense dollars per revenue dollar, provided the period and accounting scope match.
Cost income ratio = Noninterest operating expense / (Net interest income + Noninterest income)
Net interest income = Interest income − Interest expense
Multiply the quotient by 100 to display a percentage. In this formula, operating income means the revenue denominator before operating expense, provisions, and income taxes. It does not mean the bottom-line profit after those charges.
There is no safe comparison without a definition. The FDIC Quarterly Banking Profile notes define its efficiency ratio using noninterest expense less intangible asset amortization, divided by net interest income plus noninterest income. That is a specific adjustment to the numerator, not permission to remove any expense management dislikes.
For the unadjusted calculation below, keep intangible amortization in noninterest expense. Exclude interest expense from the numerator because it is already deducted in net interest income. Keep credit loss provisions and income tax expense outside both operating expense and operating revenue in this definition.
If your reporting pack removes securities gains, acquisition charges, or other items, publish the adjustment bridge. Compare periods under the same policy. A label such as adjusted efficiency ratio does not explain the calculation by itself.
Start with the management income statement export. Each row should identify the reporting period, business unit, account, amount, and inclusion category. Keep a separate mapping for interest income, interest expense, noninterest income, noninterest expense, provisions, and taxes.
Show expenses as positive amounts in the calculation, even if the export stores debits and credits differently. Retain a tie to the signed ledger so a sign conversion cannot silently inflate revenue.
For business-unit comparisons, document shared-service allocations, internal funding charges, and elimination entries. An internal unit ratio can be useful without being directly comparable to a published bank ratio. The unit's denominator may depend on allocation policies as much as on external customer revenue.
This bank measure differs from customer cost to serve, which assigns service costs to accounts or customers. It also differs from the investment income ratio, which answers a separate income question.
The following illustrative quarter has two units. Both use the same internal expense definition, and all listed amounts are USD. The example assumes no consolidation eliminations; a real workbook must include them when necessary.
| Financial line | Retail banking (USD) | Commercial banking (USD) | Total (USD) |
|---|---|---|---|
| Interest income | 6,000,000 | 4,000,000 | 10,000,000 |
| Less: interest expense | 2,000,000 | 1,000,000 | 3,000,000 |
| Net interest income | 4,000,000 | 3,000,000 | 7,000,000 |
| Noninterest income | 1,000,000 | 1,000,000 | 2,000,000 |
| Operating revenue | 5,000,000 | 4,000,000 | 9,000,000 |
| Noninterest expense | 3,250,000 | 2,000,000 | 5,250,000 |
| Cost income ratio | 65.00% | 50.00% | 58.33% |
| Intangible amortization included above | 60,000 | 40,000 | 100,000 |
| Expense excluding that amortization | 3,190,000 | 1,960,000 | 5,150,000 |
| Ratio excluding that amortization | 63.80% | 49.00% | 57.22% |
Retail operating revenue is 6,000,000 − 2,000,000 + 1,000,000 = $5,000,000. Divide its $3,250,000 expense by that revenue to get 65.00%. Commercial banking gives 2,000,000 / 4,000,000 = 50.00%.
The consolidated internal ratio is 5,250,000 / 9,000,000 = 58.33%, rounded to two decimal places. The average of 65.00% and 50.00% is 57.50%, which gives unequal-sized units equal weight and is not the consolidated ratio.
The amortization adjustment changes the numerator to 5,250,000 − 100,000 = $5,150,000. The corresponding ratio is 5,150,000 / 9,000,000 = 57.22%. Keep this adjusted result labeled separately from the internal unadjusted figure.
With interest income in B2, interest expense in B3, net interest income in B4, noninterest income in B5, operating revenue in B6, and noninterest expense in B7, enter these formulas in B4, B6, and B8, respectively:
=B2-B3
=B4+B5
=B7/B6
Format B8 as a percentage and repeat the formulas for each unit. For consolidation, add unit revenue and expense first, including any eliminations, then divide those totals.
As an independent check, place the unit revenues in H2:H3 and full-precision ratios in I2:I3:
=SUMPRODUCT(H2:H3,I2:I3)/SUM(H2:H3)
It returns the same 58.33% after display rounding. Microsoft documents SUMPRODUCT as summing the products of corresponding arrays. Covirage is not affiliated with Microsoft.
Finally, reconcile interest income less interest expense to the reported net interest income, and reconcile each inclusion category to the management income statement. A correct formula on an incomplete mapping still produces an incomplete ratio.
Hold expense at $5,250,000 and reduce operating revenue from $9,000,000 to $8,400,000 in a second illustrative quarter. Revenue falls by $600,000, or 6.67%, and the ratio rises to 5,250,000 / 8,400,000 = 62.50%. The increase is 4.17 percentage points using unrounded ratios.
The arithmetic shows a denominator change with unchanged spending. It does not establish why revenue fell. Finance should separate net interest income from fee movements, then review business volume, pricing, and internal allocations with the responsible unit leaders.
To maintain the original unrounded ratio on the lower revenue, expense would need to be (5,250,000 / 9,000,000) × 8,400,000 = $4,900,000. The implied gap is $350,000. Treat that as a planning sensitivity, not evidence that those expenses can be removed without affecting service or revenue.
The reporting discipline fits the broader work of finance teams: identify the component that moved, reconcile it, and assign an owner who can investigate the rows.
Upload the financial workbook with unit, period, account mapping, and adjustment rows; Covirage maps the columns, and its tools compute and check the ratios. The external AI model explains the changes with every figure traced to its rows. Create a free Covirage account and bring a sample of your own data; creating the account takes about a minute.
See Covirage for FP&A reporting for the supporting reporting context.
They describe closely related measures, but published definitions can differ. The FDIC efficiency ratio excludes intangible asset amortization from noninterest expense. An internal cost income ratio may retain it. Reconcile the adjustment before comparing the two figures.
In the definition used here, interest expense is deducted from interest income to calculate net interest income in the denominator. The numerator contains noninterest operating expenses. Putting interest expense in both locations would change the definition and count its effect twice.
Yes. Lower net interest income or fee income reduces the denominator, so the same expense produces a higher ratio. Separate revenue changes from expense changes before describing a deterioration as a spending problem or setting a cost reduction target.