# Simple example: mint & balanceOf
### `AToken::balanceOf` returns:
```solidity
super.balanceOf(userAddress) * POOL.getReserveNormalisedIncome(_underlyingAsset)
```
### AToken employs a unit increase model
* deposit 1 DAI -> user receives 1 aDAI
* interest is accumulated over time
* user's aDAI balance increases, reflecting incrementing interest
* 1 aDAI -> 1.5 aDAI
* user redeems aTokens 1:1 with underlying
* can redeem 1.5 DAI
### On deposit/supply:
User's deposit is recorded as "scaledBalance":
$$scaledBalance = \frac{amountDeposited}{currentLiquidityIndex}$$
scaledBalance is the actual value stored on-chain, within `_userState[userAddress].balance`.
{% hint style="info" %}
All deposits are scaled against the liqudity index and stored as scaled values via `_userState[userAddress].balance`
{% endhint %}
**Example**
### mint
The user is minted aTokens according to the scaledBalance, not the deposit value.
* however, balanceOf is calculated by scaling up the scaledBalance against the incrementing liquidity index.
* this is why, from the end-user's perspective it looks like they have minted aToken 1:1 to their deposits, and
* their aToken balance continually increments over time - because the liquidity index increments
### AToken balance
```solidity
aTokenBalance = scaledBalance * currLiquidityIndex
```
* LiquidityIndex only increments
* An account's aTokenBalance can never go down, unless a withdrawal occurs
**Simplified illustration:**
```solidity
super.balanceOf(userAddress) * POOL.getReserveNormalisedIncome(_underlyingAsset)
_userState[userAddress].balance * reserve.LiquidityIndex
scaledBalance * currLiquidityIndex
```
**Links**
*
*
