What it means
Banks are unusual businesses because most of the money they lend belongs to depositors and bondholders rather than to shareholders. Capital is the shareholders' own stake, the cushion that absorbs losses before anyone else's money is at risk, and tier 1 is the part of that cushion that is genuinely permanent and loss-absorbing.
The denominator is not total assets but risk-weighted assets, which is a deliberate design choice. A government bond and an unsecured business loan of the same size carry very different risks, so each asset is multiplied by a weighting before being added up, meaning a bank full of safe assets needs less capital than one full of risky ones.
Tier 1 splits into two parts. Common equity tier 1, usually abbreviated to CET1, is ordinary shares and retained earnings, while additional tier 1 consists of specific perpetual instruments that convert to equity or are written down if the bank gets into trouble.
The internationally agreed minimum under the Basel framework is 6% for total tier 1 and 4.5% for CET1, before the extra buffers regulators pile on top. In practice large banks operate well above these floors, often reporting CET1 ratios between 12% and 16%, partly because falling near the minimum restricts dividends and bonuses.
For anyone outside banking the ratio is still worth understanding, because it tells you how much appetite your bank has for lending. When capital ratios come under pressure, banks tighten credit, reprice loans and withdraw facilities, and that shows up in your borrowing costs long before it makes the news.
In practice
Real-world examples.
Example
A bank reports a CET1 ratio of 11.2% against a regulatory requirement of 10.5% and cancels its planned share buyback. The board judges that operating with only 0.7 percentage points of headroom leaves no room for a downturn in the loan book.
Example
A corporate treasurer choosing between two lenders for a five year facility compares their tier 1 ratios alongside pricing. The cheaper lender is running noticeably thinner capital, which raises the risk that the facility is repriced or not renewed.
Example
A supervisor completing a stress test tells a bank its tier 1 ratio would fall from 13% to 7.5% under a severe recession scenario. The bank responds by retaining more profit and slowing growth in unsecured lending.
Think of it
“Tier 1 ratio shows a bank's strongest capital cushion against risky assets-the key safety metric.
Formula
Calculation
Tier 1 capital ratio = Tier 1 capital / Risk-weighted assets
A regional bank holds common equity tier 1 capital of $8,400,000,000 and additional tier 1 instruments of $1,200,000,000, so total tier 1 capital is $8,400,000,000 + $1,200,000,000 = $9,600,000,000.
Its risk-weighted assets total $120,000,000,000. The tier 1 capital ratio is $9,600,000,000 / $120,000,000,000 = 0.08, or 8%, and the CET1 ratio separately is $8,400,000,000 / $120,000,000,000 = 0.07, or 7%.
Both sit above the Basel minimums of 6% and 4.5%, but the headroom is thin. If loan losses of $1,200,000,000 wiped out the additional tier 1 layer, the tier 1 ratio would fall to $8,400,000,000 / $120,000,000,000 = 7%, and regulators would expect a capital raising plan rather than a dividend.Case study
Seen in the real world.
The following is an illustrative and entirely fictional example. Kestrel Regional Bank, an invented lender, spent three years growing its commercial property book at 20% a year while paying out most of its profit as dividends. Its tier 1 ratio drifted from 12.5% down to 8.9% without anyone treating the trend as urgent.
Property values in its main region then fell, and risk weightings on the affected loans increased in this fictional scenario. Risk-weighted assets rose even though the loan balances had not, and the tier 1 ratio fell to 7.4%, close enough to the regulatory floor that the supervisor imposed restrictions on distributions.
Kestrel's illustrative board suspended the dividend, raised $400,000,000 of new equity at a price well below the previous year's, and stopped writing new commercial property loans for eighteen months. The lesson drawn afterwards was that capital ratios need to be managed with a buffer for bad times rather than optimised for good ones.
Watch out
Common mistakes.
- Comparing the tier 1 ratio to total assets rather than risk-weighted assets, which produces a much smaller number that means something entirely different.
- Assuming a ratio comfortably above the minimum is safe, without asking how it behaves under a stress scenario.
- Treating tier 1 and CET1 as interchangeable, when CET1 is the stricter and more closely watched of the two.
Questions
People also ask.
What counts as tier 1 capital?
Ordinary shares, share premium and retained earnings make up common equity tier 1, with certain perpetual loss-absorbing instruments counted as additional tier 1.
Why do risk weights matter so much?
Because they decide the size of the denominator, so a shift towards riskier lending can cut the ratio even when no new money has been lent.
Should a business customer care about its bank's ratio?
Yes, since a bank under capital pressure typically reduces lending, raises pricing and declines to renew facilities, all of which affect your funding.
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