How to calculate the reducible balance of a user?

Question

I would like to ask question about free balance on Kusama

when we execute the query

await api.query.system.account('some address')

then the output is this

{
  nonce: 1
  consumers: 0
  providers: 1
  sufficients: 0
  data: {
    free: 899,973,503,629,159
    reserved: 0
    miscFrozen: 0
    feeFrozen: 0
  }
}

My question is what is the true FREE balance ?

Because when the user have some frozen .. it means he/she cannot go below the frozen limit So the true FREE balance is FREE - MISCFROZEN - FEEFROZEN ?

Answer 1

Seems like you are looking to calculate the current "reducible" balance of a user, which has a function defined in the Balances Pallet:

fn reducible_balance(who: &T::AccountId, keep_alive: bool) -> Self::Balance {
    let a = Self::account(who);
    // Liquid balance is what is neither reserved nor locked/frozen.
    let liquid = a.free.saturating_sub(a.fee_frozen.max(a.misc_frozen));
    if frame_system::Pallet::<T>::can_dec_provider(who) && !keep_alive {
        liquid
    } else {
        // `must_remain_to_exist` is the part of liquid balance which must remain to keep total
        // over ED.
        let must_remain_to_exist =
            T::ExistentialDeposit::get().saturating_sub(a.total() - liquid);
        liquid.saturating_sub(must_remain_to_exist)
    }
}

So this is the logic you want to use.

It is important to note that FROZEN funds are not cummulative, so the simple calculation would be:

FREE - max(MISCFROZEN, FEEFROZEN)

as seen in the liquid calculation. But you should also take into account whether you allow the account to die or not.