Account Balances

Reading the balance of an account is pretty simple; call the BalanceAt method of the client passing it the account address and optional block number. Setting nil as the block number will return the latest balance.

account := common.HexToAddress("0x71c7656ec7ab88b098defb751b7401b5f6d8976f")
balance, err := client.BalanceAt(context.Background(), account, nil)
if err != nil {
  log.Fatal(err)
}

fmt.Println(balance) // 25893180161173005034

Passing the block number let's you read the account balance at the time of that block. The block number must be a big.Int.

blockNumber := big.NewInt(5532993)
balance, err := client.BalanceAt(context.Background(), account, blockNumber)
if err != nil {
  log.Fatal(err)
}

fmt.Println(balance) // 25729324269165216042

Numbers in ethereum are dealt using the smallest possible unit because they're fixed-point precision, which in the case of ETH it's wei. To read the ETH value you must do the calculation wei / 10^18. Because we're dealing with big numbers we'll have to import the native Go math and math/big packages. Here's how'd you do the conversion.

fbalance := new(big.Float)
fbalance.SetString(balance.String())
ethValue := new(big.Float).Quo(fbalance, big.NewFloat(math.Pow10(18)))

fmt.Println(ethValue) // 25.729324269165216041

Pending balance

Sometimes you'll want to know what the pending account balance is, for example after submitting or waiting for a transaction to be confirmed. The client provides a similar method to BalanceAt called PendingBalanceAt which accepts the account address as a parameter.

pendingBalance, err := client.PendingBalanceAt(context.Background(), account)
fmt.Println(pendingBalance) // 25729324269165216042

Full code

account_balance.go

package main

import (
    "context"
    "fmt"
    "log"
    "math"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/ethclient"
)

func main() {
    client, err := ethclient.Dial("https://cloudflare-eth.com")
    if err != nil {
        log.Fatal(err)
    }

    account := common.HexToAddress("0x71c7656ec7ab88b098defb751b7401b5f6d8976f")
    balance, err := client.BalanceAt(context.Background(), account, nil)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(balance) // 25893180161173005034

    blockNumber := big.NewInt(5532993)
    balanceAt, err := client.BalanceAt(context.Background(), account, blockNumber)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(balanceAt) // 25729324269165216042

    fbalance := new(big.Float)
    fbalance.SetString(balanceAt.String())
    ethValue := new(big.Float).Quo(fbalance, big.NewFloat(math.Pow10(18)))
    fmt.Println(ethValue) // 25.729324269165216041

    pendingBalance, err := client.PendingBalanceAt(context.Background(), account)
    fmt.Println(pendingBalance) // 25729324269165216042
}