Free calculator
How much can you spend today?
Not what’s in your account — what’s actually yours to spend once everything already spoken for is out of the way.
Your numbers
Four inputs. That’s the whole thing.
What actually lands in your account each month, after tax.
Rent, utilities, phone, insurance, subscriptions — anything that hits on a schedule.
What you put toward cards or loans. Zero is a fine answer.
Set aside for the non-recurring stuff — a concert, a flight, a good dinner out.
Your Flow
Buck breaks your income down the same way the app does, then divides what's genuinely yours to spend by the days left in the month.
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How the math works
Most budgeting advice starts by asking you to sort your life into twenty categories. Buck starts somewhere simpler: of the money that arrives this month, how much is genuinely free?
It runs as a waterfall. Take-home pay comes in at the top. Out goes everything already committed — rent, utilities, insurance, subscriptions. Then a 5% cushion, which is forced savings routed toward debt or a buffer, not an expense. Then whatever you’ve chosen to put toward debt above the minimum. Then a treat fund for the non-recurring things that would otherwise blow up an ordinary week.
What survives is your discretionary pool. Divide it by the days left in the month and you get Flow — what today is worth.
The important part is what happens next. Flow is self-correcting: it divides what’s remaining by the days remaining, so a $200 night out doesn’t become a moral failure, it just makes tomorrow slightly smaller. A quiet week does the reverse. You never have to rebuild a budget — the number absorbs reality on its own.
This calculator works from four numbers you type. The app does the same math against your real transactions, updates it daily, and tells you where you stand before the month is already spent.