[Question] How to accurately calculate the transfer fee?

[mahnunchik]

Hello, I've faced with the issue that estimated fee doesn't math the real fee paid for the transfer.

import { WalletContractV4, TonClient, internal } from '@ton/ton';

const client = new TonClient({
  endpoint: 'https://testnet.toncenter.com/api/v2/jsonRPC',
});

const wallet = WalletContractV4.create({
  publicKey: key.publicKey,
  workchain: 0,
});

const walletContract = client.open(wallet);
const seqno = await walletContract.getSeqno();

const transfer = await walletContract.createTransfer({
  secretKey: key.secretKey,
  seqno: seqno,
  messages: [
    internal({
      to: secondAddress,
      value: sendAmount,
      body: "Hello",
      bounce: false,
    })
  ],
});

console.log('estimate:', await client.estimateExternalMessageFee(wallet.address, { body: transfer } ));

await walletContract.send(transfer);

Estimation output

{
  '@type': 'query.fees',
  source_fees: {
    '@type': 'fees',
    in_fwd_fee: 1564000,
    storage_fee: 108763,
    gas_fee: 3308000,
    fwd_fee: 1000000
  }
}

Sum of storage_fee + in_fwd_fee + fwd_fee + gas_fee equals 5980763 which is 3 gram less then real fee paid for the transaction https://testnet.tonscan.org/tx/2xRWxV-7sIxMWpT8xmLGYgc5Z8YOk93GZVURJzw2Ro0= (0,005980766 TON = 5980766).

Fee estimation shortage may differ from 2 to 100 grams, but always less then real fee.

How to accurately calculate the transfer fee?

[mahnunchik]

Related issue: toncenter/tonweb#124

[mahnunchik]

@dvlkv any ideas?

[dvlkv]

Hi! Have you tried to use computeExternalMessageFees, computeFwdFees, computeGasPrices, computeMessageForwardFees, computeStorageFees provided by library? You can find examples here: fees.spec.ts