What it means
The core problem is mismatch in two dimensions: timing and rate sensitivity. A bank might hold twenty-five year mortgages funded by deposits repayable on demand, and a pension scheme might owe payments in forty years while holding bonds maturing in ten.
Asset/liability management is the discipline of measuring those mismatches and deciding how much of each to accept. It matters because the mismatch is where the earnings and the danger both come from.
Borrowing short and lending long is profitable in normal conditions precisely because it carries risk, and institutions that eliminate the mismatch entirely usually eliminate their margin too. The task is calibration rather than elimination.
Practitioners use a layered toolkit. Repricing gap analysis buckets assets and liabilities by when their rates reset, duration analysis measures how sensitive values are to a rate change, cash flow projections test whether obligations can be met week by week, and stress tests and scenario analysis explore what happens under severe but plausible conditions.
Each tool answers a different question and none is sufficient alone. The levers available are equally practical.
An institution can change the maturity mix of its lending and funding, alter deposit or premium pricing, buy and sell securities, and use derivatives such as interest rate swaps, caps and floors to reshape exposure without changing the underlying business. Insurers and pension schemes often go further with cash flow matching or immunisation, deliberately buying assets whose payments mirror their obligations.
Behaviour is the hardest input to get right. Customers repay mortgages early when rates fall, deposits described as instant access often sit untouched for years, and policyholders surrender contracts at inconvenient moments, so contractual maturities can be very misleading.
Good asset/liability management models expected behaviour and then tests what happens if that behaviour changes suddenly.
In practice
Real-world examples
Example 1
A pension scheme with payments stretching forty years ahead buys long-dated index-linked government bonds so its assets move roughly in step with its obligations. When long-term rates fall and the value of its liabilities jumps, the bond portfolio rises too. The funding level stays broadly stable.
Example 2
A bank with a large fixed-rate mortgage book enters interest rate swaps, paying fixed and receiving floating on $300,000,000 of notional. The swap converts the economics of the fixed lending into something closer to its floating-rate funding. The mortgage customers see no change at all.
Example 3
A general insurer holds short-dated bonds and cash against motor claims that are typically settled within eighteen months. Matching the maturity of the investments to the expected claims pattern means it never has to sell assets at a loss to pay a claim. Longer bonds are reserved for the liability lines that settle slowly.
Think of it
Imagine driving a manual car. Your assets are the fuel in the tank, while your liabilities are the hills ahead that require effort to climb. Asset liability management is the skill of shifting gears at the right time so you never stall.
Formula
Calculation
Duration Gap = Asset Duration - ((Total Liabilities / Total Assets) x Liability Duration)
Approximate Change in Equity Value = -Duration Gap x Total Assets x Change in Interest Rate
Thornbury Savings Bank has assets of $900,000,000 with an average duration of 4.5 years, and liabilities of $810,000,000 with an average duration of 2.0 years. Equity is therefore $900,000,000 - $810,000,000 = $90,000,000.
Liabilities as a share of assets = $810,000,000 / $900,000,000 = 0.9.
Duration gap = 4.5 - (0.9 x 2.0) = 4.5 - 1.8 = 2.7 years.
If interest rates rise by 1%, the approximate change in the economic value of equity = -2.7 x $900,000,000 x 0.01 = -$24,300,000. That is $24,300,000 / $90,000,000 = 27% of the bank's equity wiped out by a one percentage point move, which almost any board would consider far too much. Closing the gap, by shortening asset duration or lengthening liability duration, is exactly the kind of decision asset/liability management exists to force.Case study
Seen in the real world
Larkfield Building Society is an illustrative, fictional lender used to show the duration gap in action. It held $600,000,000 of assets with an average duration of 5.0 years, funded by $540,000,000 of liabilities with an average duration of 2.0 years, leaving equity of $60,000,000.
The duration gap was 5.0 - ((540 / 600) x 2.0) = 5.0 - 1.8 = 3.2 years. A one percentage point rise in rates would reduce the economic value of equity by roughly 3.2 x $600,000,000 x 0.01 = $19,200,000, which is 32% of the society's entire equity base. The board had never seen the exposure expressed that way, because the accounting profit looked perfectly healthy.
Over the following year the society sold longer-dated fixed-rate assets, added swaps and shifted new lending towards trackers, bringing asset duration down to 3.0 years. The gap fell to 3.0 - 1.8 = 1.2 years, so the same one percentage point rise would cost about $7,200,000, or 12% of equity. Margin was slightly lower, which is the trade every asset/liability decision comes down to.
Watch out
Common mistakes
- Using contractual maturities for deposits and loans instead of modelled behaviour, which understates how long instant-access balances really stay and how fast mortgages are repaid early.
- Relying on a single measure such as the repricing gap, when it says nothing about what happens to the economic value of longer-dated positions.
- Treating asset/liability management as a reporting exercise for the risk team rather than a set of decisions that change pricing, lending and funding.
Questions
People also ask
Is the goal to eliminate all mismatch?
No, some mismatch is the source of the margin, so the goal is to keep it within limits the board has explicitly approved and can afford.
What is the difference between duration gap and repricing gap?
Repricing gap looks at how much reprices within a time bucket and affects near-term income, while duration gap measures the sensitivity of economic value across the whole balance sheet.
Do non-financial companies do this?
Yes in simplified form, whenever a treasury team matches the maturity of borrowings to the assets they fund or hedges floating-rate debt to protect a budget.