Lending market rate curves: the kink, utilization, and why suppliers watch it

There is no committee behind an on-chain lending rate. Each market publishes a function that maps utilization, the share of supplied assets currently borrowed, to a borrow rate, and the supply rate follows from it. The function is visible in the contract, the utilization is visible on-chain, and anyone can compute what the rate will be at any level of demand before demand gets there.

That transparency is the point of the design and the source of most of the discipline a supplier needs.

The shape of the curve

Compound’s documentation describes the model most protocols share: below a utilization threshold the rate rises slowly with utilization, and above it the rate increases far more rapidly. The threshold is the kink. Aave’s model expresses the same idea as an optimal utilization with two slopes, a shallow one below and a steep one above. The steep segment exists to defend the market’s liquidity: when nearly everything supplied has been borrowed, a sharp rise in the borrow rate pushes borrowers to repay and pulls in new supply, restoring the buffer that lets suppliers withdraw.

Morpho’s adaptive curve takes the idea a step further. Its rate model has the same curved response to utilization in the short run, and in addition shifts the whole curve up or down over time when utilization sits persistently away from a target, so that the market finds a rate at which supply and demand balance rather than relying on the kink alone.

Why suppliers watch utilization, not just rate

A supplier can withdraw only what has not been borrowed. At full utilization there is nothing to withdraw, and a supplier who wants out has to wait for a borrower to repay or for the steep rate to attract new supply. The supply rate at that moment is the highest it will ever be, which is exactly why a rate on its own is a poor guide. A market paying an unusually high supply rate is a market close to the point at which withdrawals stall.

• Utilization: borrowed divided by supplied; the single input to the rate function
• Kink or optimal utilization: the level above which the rate slope steepens sharply
• Available liquidity: supplied minus borrowed; what a supplier can actually withdraw right now
• Reserve factor: the share of interest retained by the protocol rather than paid to suppliers

Reading a spike

Supply rates jump for two very different reasons. In the first, borrowing demand has risen: a rally has increased the appetite for leveraged dollars, or a new opportunity is being financed, and utilization has crossed the kink from below. Rates will fall as supply arrives, and a supplier who enters early earns the spike and leaves before it normalizes. In the second, supply has left: suppliers are withdrawing because something has frightened them, utilization has crossed the kink from above, and the high rate is the market pleading for liquidity it may not get. The number on the screen is the same. The right action is the opposite.

Telling the two apart means looking at the flows behind utilization rather than the ratio itself: whether borrowed balances are growing or supplied balances are shrinking, whether the change is concentrated in a few large accounts, and what is happening to the collateral that backs the borrowing. It also means knowing the market’s depth. A rate spike in a market where the supplier’s position is a large share of available liquidity is not an opportunity, because the act of leaving would move the rate the supplier came for.

Curves as a source of relative value

Because every market publishes its own function, the same asset lends at different rates across protocols and chains at the same moment, and part of that gap is simply capital that has not moved. A supplier who compares curves, not just current rates, can see where a modest inflow would compress the rate and where it would not. The comparison has to be net of the cost of moving and honest about the risk difference between the two markets. A higher rate on a thinner market with a weaker oracle is not a dislocation. It is a price.

The rate curve is the most public fact about an on-chain lending market and the least read. It tells a supplier what they will earn, what they can withdraw, and what the market will do to itself if demand keeps rising. Watching it is most of the job.