> ## Documentation Index
> Fetch the complete documentation index at: https://dev.jup.ag/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Compute Units & Priority Fees

> Control compute unit limits and priority fee percentiles on /build

The `/build` response includes `computeBudgetInstructions` with the **compute unit price** but not the **compute unit limit**. You need to simulate to determine the correct limit.

Why: since you are building your own transaction with custom instructions, the CU usage will differ from a base swap. The simulation gives you the actual number, and you set the limit with a safety buffer.

## Why this matters

Priority fee cost is calculated as:

```
priority fee = compute unit price × compute unit limit
```

A tighter CU limit directly reduces the priority fee you pay. Setting it to the maximum (1,400,000) when you only use 200,000 means you pay 7x more than necessary. See [Solana fee structure](https://solana.com/docs/core/fees/fee-structure) for details.

## Customise compute unit price

The `/build` response bakes a compute unit price into `computeBudgetInstructions` based on recent network priority fees. Use `computeUnitPricePercentile` to control how aggressively you bid:

| Value           | Percentile      | Use case                                      |
| --------------- | --------------- | --------------------------------------------- |
| `"medium"`      | 25th            | Lower fees, may land slower during congestion |
| `"high"`        | 50th            | Balanced (default)                            |
| `"veryHigh"`    | 75th            | Higher fees, better chance of landing quickly |
| Integer 0-10000 | Custom (in bps) | Fine-grained control                          |

When `mode=fast` is set and no `computeUnitPricePercentile` is provided, the default is the 90th percentile instead of the 50th.

You can also override entirely by replacing the `computeBudgetInstructions` from the response with your own `setComputeUnitPrice` instruction.

## Estimate compute unit limit

1. Build the transaction with all your instructions + **max CU limit** (1,400,000)
2. Simulate with `replaceRecentBlockhash: true` to get actual CU consumed
3. Rebuild with **1.2x the simulated value** (capped at 1,400,000) as the CU limit
4. Add the CU price instruction from the `/build` response

The [Build](/swap/build) code example demonstrates this in steps 4-5 (kit) with full working code.

<Warning>
  Setting the CU limit too tight causes transaction failures. Always use at least a 1.2x buffer over the simulated value.
</Warning>

## Related

* [Build](/swap/build) for the full code example with CU simulation
* [Transaction Submission](/transaction/submit) to submit via Jupiter's transaction landing infrastructure with SOL tips for priority processing
* [Reduce Transaction Size](/swap/advanced/reduce-transaction-size) for other optimisations