---
title: account_transfer
description: Transfers balance between two accounts
source_url:
  html: https://thru.org/docs/spec/vm/syscalls/account_transfer/
  md: https://thru.org/docs/spec/vm/syscalls/account_transfer.md
---

# account_transfer

## Overview

The `account_transfer` syscall transfers a specified amount of balance from one account to another. Both accounts must exist and meet writability requirements.

## Syscall Code

**Code:** `0x03` (`TN_SYSCALL_CODE_ACCOUNT_TRANSFER`)

## C SDK Function

```c
ulong tsys_account_transfer(ulong from_account_idx, ulong to_account_idx, ulong amount);
```

## Arguments

**`from_account_idx` · *ulong* · **required****

Index of the source account to transfer balance from. Must be writable by the current program.

**`to_account_idx` · *ulong* · **required****

Index of the destination account to transfer balance to. Must be writable in the transaction.

**`amount` · *ulong* · **required****

Amount of balance to transfer from source to destination account.

## Return Value

Returns a syscall result code:

**`Success` · *ulong***

- `TN_VM_SYSCALL_SUCCESS` (0) - Transfer completed successfully

**`Error Codes` · *ulong***

- `TN_VM_ERR_SYSCALL_INVALID_ACCOUNT_INDEX` (-8) - Invalid from or to account index
- `TN_VM_ERR_SYSCALL_ACCOUNT_NOT_WRITABLE` (-10) - From account not writable by program or to account not writable in transaction
- `TN_VM_ERR_SYSCALL_ACCOUNT_DOES_NOT_EXIST` (-9) - Source or destination account does not exist
- `TN_VM_ERR_SYSCALL_INSUFFICIENT_BALANCE` (-38) - Source account has insufficient balance
- `TN_VM_ERR_SYSCALL_INVALID_ACCOUNT` (-27) - Either account is ephemeral (not allowed for transfers)
- `TN_VM_ERR_SYSCALL_BALANCE_OVERFLOW` (-11) - Destination balance would overflow

## Resource Consumption

### Compute Units

- **Base cost**: `TN_VM_SYSCALL_BASE_COST` (512 units)
- **Additional cost**: None
- **Total cost**: Fixed at 512 units regardless of transfer amount

### Memory Pages

- **Page usage**: No direct page allocation or deallocation
- **Metadata impact**: May trigger metadata page allocation for both accounts if not already writable

## Side Effects

- **Balance modification**: Decreases source account balance and increases destination balance
- **Account metadata**: Makes account metadata writable if not already

## Usage Notes

- Both accounts must be non-ephemeral accounts
- Source account must be writable by the current program
- Destination account must be writable in the transaction (signer approval)
- Transfer amount cannot exceed source account balance
- Destination balance cannot overflow (exceed maximum value)
- Account metadata is automatically made writable for both accounts

## Example

```c
#include <thru-sdk/c/tn_sdk_syscall.h>

// Transfer 1000 units from account 0 to account 1
ulong from_account = 0;
ulong to_account = 1;
ulong amount = 1000;

ulong result = tsys_account_transfer(from_account, to_account, amount);

if (result == TN_VM_SYSCALL_SUCCESS) {
    // Transfer completed successfully
    // from_account balance decreased by 1000
    // to_account balance increased by 1000
}
```