How Are DeFi Interest Rates Determined? Explained

DeFi interest rates are typically determined algorithmically by a lending protocol's utilization-based interest rate curve — a formula that sets the borrow rate as a function of how much of a pool's supplied assets are currently borrowed, with the supply rate derived from that borrow rate minus a protocol fee.

Why algorithmic rates instead of a fixed number

A money market protocol has no central authority deciding "the rate for USDC today is X%." Instead, rates emerge from a transparent formula applied to real-time on-chain data: the ratio of borrowed assets to total supplied assets in a given pool, known as the utilization rate. This makes rates self-adjusting and resistant to manipulation by any single party — the formula reacts to actual market conditions rather than a decision made by anyone.

The utilization rate

Utilization is simply the percentage of supplied assets currently borrowed out: if a pool has 100 units supplied and 60 borrowed, utilization is 60%. This single number drives the entire rate curve, because it's the clearest available signal of how much demand there is for borrowing that specific asset relative to available supply.

The typical shape of the curve

Most protocols use a piecewise curve with two segments, meeting at a defined "kink" point (often somewhere between 80–90% utilization, though this varies by asset and protocol):

• Below the kink — the borrow rate rises gradually and predictably as utilization increases, keeping rates reasonable for normal market conditions.
• Above the kink — the borrow rate rises much more steeply, sometimes dramatically, as utilization approaches 100%. This sharp increase is deliberate: it strongly discourages further borrowing and strongly incentivizes new supply or debt repayment, protecting the pool from a scenario where utilization hits 100% and remaining suppliers can't withdraw at all.

From borrow rate to supply rate

The supply rate isn't set independently — it's derived directly from the borrow rate and the utilization rate, since supply rate revenue comes entirely from what borrowers pay. Roughly: supply rate equals the borrow rate multiplied by utilization, minus whatever percentage the protocol keeps as a fee (the "reserve factor"). This is why supply rates are always lower than borrow rates for the same asset — the gap is the protocol's cut plus the mathematical effect of utilization being less than 100%.

A simplified example

Utilization	Typical borrow rate behavior	Effect on supply rate
Low (e.g., 20%)	Low, near the curve's base rate	Low — few borrowers paying interest to few suppliers
Moderate (e.g., 60%)	Rising steadily along the curve	Rising — more borrowed assets generating interest
Near the kink (e.g., 85%)	Approaching the curve's inflection point	Near its highest sustainable point
Above the kink (e.g., 95%+)	Spikes sharply	Also spikes, but liquidity for withdrawal becomes scarce

Why this matters for both sides

For lenders, understanding the curve explains why supply rates on the yield dashboard can look attractive one day and much lower the next — they move with real borrowing demand, not a fixed schedule. A high advertised rate on a low-utilization pool can look appealing but may not be sustainable if utilization later drops.

For borrowers, the steep rate increase above the kink is a genuine risk factor, separate from liquidation risk: even a fully healthy, well-collateralized position can become expensive to hold if utilization spikes and the borrow rate climbs sharply, which matters for anyone borrowing for an extended period rather than a short-term trade.

Who sets the curve's parameters

The specific shape of a utilization curve — the base rate, the slope on each segment, and where the kink sits — isn't universal; it's chosen per asset, usually by the protocol's governance process or by whoever configures a specific isolated market. A stablecoin market might use a curve with a high kink point (since utilization can safely run higher before liquidity becomes a real concern) and a gentle slope below it, while a market for a more volatile or thinly traded asset might use a lower kink and steeper slope, reflecting the greater danger of a liquidity crunch. This is why the same protocol can show meaningfully different rate behavior across its different markets even though the underlying formula structure is the same.

Fixed-rate alternatives

Some protocols and products offer fixed or tokenized-yield alternatives that let users lock in a specific rate rather than being exposed to a floating utilization-driven rate, trading potential upside from favorable rate movements for predictability — a trade-off explored further in our comparison of Pendle vs. Yearn yield strategies.

Bottom line

DeFi interest rates aren't set by a company or committee — they're computed continuously from a transparent utilization-based formula that automatically balances supplier and borrower incentives. Understanding the shape of this curve, and specifically where the "kink" sits, helps explain both why yields fluctuate and why borrowing costs can spike sharply during periods of high demand. Always check a market's current utilization alongside its advertised rate on the yield dashboard before assuming today's rate will hold tomorrow.