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# Algorand Specifications

When the TxPool becomes congested, a _fee prioritization_ algorithm determines which transactions are enqueued into the pool and which are rejected.

The key parameter in this process is `feePerByte`, which is calculated dynamically based on the number of pending blocks awaiting evaluation.

The `pendingFullBlocks` is an unsigned integer that represents the number of uncommitted full blocks present in the `TxPool`.

The function `computeFeePerByte` below demonstrates how this value is computed:

* * *

### Algorithm 2: Compute Fee per Byte

1:  function `ComputeFeePerByte()`  
2:      `feePerByte` ← `feeThresholdMultiplier`  
3:      if `feePerByte = 0 ∧ TxPool.pendingFullBlocks > 1` then  
4:          `feePerByte` ← 1  
5:      end if  
6:      for `i` from 0 to `TxPool.pendingFullBlocks` do  
7:          `feePerByte` ← `feePerByte` ⋅ `TxPool.expFeeFactor`  
8:      end for  
9:      return `feePerByte`  
10: end function

* * *

> Important  
> **IMPLEMENTATION:**  
> Compute fee per byte [reference implementation](https://github.com/algorand/go-algorand/blob/b6e5bcadf0ad3861d4805c51cbf3f695c38a93b7/data/pools/transactionPool.go#L328).

The `computeFeePerByte` function begins by setting `feePerByte` equal to the `feeThresholdMultiplier`. When there is no congestion in `TxPool`, this value is 0.

However, if there are any full blocks currently pending in `TxPool`, `feePerByte` is initially set to 1. This setup ensures that the subsequent multiplication step accumulates due to a non-zero base.

Next, for each of these full pending blocks, the `expFeeFactor` is multiplied by the current `feePerByte` value—causing `feePerByte` to grow exponentially with the level of congestion.

The resulting `feePerByte` is then:

`feePerByte = max{1, feeThresholdMultiplier} × expFeeFactor ^ {TxPool.pendingFullBlocks}`.