# Dynamic Fees

## **Objective**

Dynamic fees allow app developers to monetize usage of their app without requiring users to pay an explicit fee. Instead, users pay a multiple of the normal gas cost, and the excess is automatically transferred to the app developer.

## **Solution**

On Sonic, developers can enroll in the [Fee Monetization](/~/changes/292/funding/fee-monetization.md) program, which lets builders earn 90% of the network fees their apps generate. To benefit, developers simply need to increase the gas consumption of their contracts in a controlled manner.

The following examples outline best practices for safely increasing contract gas usage. Use the abstract contract below as a parent for your own contract:

```solidity
abstract contract DynamicGasCharging {

   uint256 private gasScalingFactor;

   /**
    * @dev Consume the given amount of gas.
    * In contract code this function can be flexibly used at any place to add extra gas consumption
    */
   function _consumeGas(uint256 gas) view internal {
       uint256 initialGas = gasleft();
       uint256 wantedGas = initialGas - gas;
       while (gasleft() > wantedGas) {
           // do nothing
       }
   }

   // Modifier to increase the gas costs of a function by a configurable multiplier
   modifier scaleGasCosts() {
       uint256 initialGas = gasleft();
       _;
       uint256 gasUsed = initialGas - gasleft();
       _consumeGas(gasUsed * (gasScalingFactor-1));
   }

   // Set the scaling factor (to be called by implementations)
   function _setGasScalingFactor(uint256 newGasScalingFactor) internal {
       gasScalingFactor = newGasScalingFactor;
   }

}
```

Once integrated, the following changes must be applied to your contract:

1. Inherit from the `DynamicGasCharging` contract.
2. Add the `scaleGasCosts` modifier to each function where dynamic gas charging should apply.
3. Set the `gasScalingFactor`—either in the contract initializer or via an `onlyOwner` function.

Example:

```solidity
contract DynamicGasExample is DynamicGasCharging, Ownable {

   function myMethod() external scaleGasCosts {
       counter++; // code of your method
   }

   function setGasScalingFactor(uint256 newGasScalingFactor) external onlyOwner {
       _setGasScalingFactor(newGasScalingFactor);
   }

}
```


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