Estimate bills for the month & transfer the rest to mutual funds
Expenses all paid by credit card, so I’m always ‘budgeting’ for the previous month and there’s no guesswork. Emergency expenses larger than a paycheck might require selling some mutual funds, but in 20 years that never happened.
Now I’m not working, budgeting is basically the same, except that interest and dividends appear at random intervals in brokerage, are no longer automatically reinvested, but transferred to checking to cover bills, usually around the same time as the paycheck used to appear.
I don’t automate anything, because I want to notice if a bill is larger than expected and address whatever caused that to happen.