What you can spend per day until your next paycheck.
Safe to spend = this month's cash left ÷ days until your next income lands. It shows on the dashboard stats strip when you're viewing the current month and have income set up.
The same cash-left figure as the Left to spend cell: income minus expected bills and one-time expenses. Safe to spend divides it by the days remaining until your next income deposit (from Settings → Income) and labels the date — "$142 / day until Aug 15".
A per-day number is meaningless for a month that's over or hasn't started, and with no income recorded there's no payday to anchor to. In both cases the stat hides itself instead of showing a number you shouldn't trust.