As discussed here, Leather would benefit from an estimated_balance property in addition to the balance as returned by the balances endpoint for a given Stacks address.

This estimated balance would subtract the total of all outbound transfers from its confirmed balance for a given address.

Leather currently calculates such a balance through two separate queries and a final calculation:

1. fetch balance from api.hiro.so/extended/v1/address/<address>/balances
2. fetch pending txs from api.hiro.so/extended/v1/tx/mempool?address=<address>&limit=50
3. do calculation: availableBalance = balance - sum of all outbound transaction amounts