# Interest rates

Each lending pool has own set of interest rate

### Utilization rate

All interest rates in Drops are determined as a function of a metric known as the **utilization rate**. The utilization rate $$U\_a$$ for a money market $$a$$ is defined as:

$$U\_a = Borrows\_a / (Cash\_a + Borrows\_a - Reserves\_a)$$

* $$Borrows\_a$$ refers to the amount of $$a$$ borrowed.
* $$Cash\_a$$ refers to the amount of $$a$$ left in the system.
* $$Reserves\_a$$ refers to the amount of $$a$$ that Drops keeps as profit.

Intuitively speaking, this is the percentage of money borrowed out of the total money supplied.

### Borrow & Supply rates

The borrowing rate's calculation depends on something called an **interest rate model** - the algorithmic model to determine a money market's borrow and supply rates.&#x20;

Borrow and supply rates are calculated using the utilization rate and several arbitrary constants.

Markets follow what is known as the "Jump Rate" model, which contains the following parameters:

* Base rate per year - the minimum borrowing rate
* Multiplier per year - the rate of increase in interest rate with respect to utilization
* Kink - the point in the model in which the model follows the jump multiplier
* Jump Multiplier per year - the rate of increase in the interest rate with respect to utilization after the "kink"

The borrow rate of the jump rate model is defined as follows:

$$
\begin{aligned} \text{Borrow Interest Rate} &= \text{Multiplier} \* min(U\_a, \text{Kink}) \ &+ \text{Jump Multiplier} \* max(0, U\_a - \text{Kink}) \ &+ \text{Base Rate} \end{aligned}
$$


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