1. What your budget still allows
Start with your budget for day-to-day spending and take off what you've already spent. If you've gone over, the answer is zero, not a negative number: overspending is money that's already gone, and you can't spend it a second time.
budget left = budget − spent (never below 0)
2. What your cash allows
A generous budget means nothing if the money isn't there. So once you enter an income, the calculator also works out how much cash you really have left this month, and takes whichever figure is lower.
cash left = income − fixed costs − loan payments − savings − spent
left this month = the lower of budget left and cash left (never below 0)
No income entered? Then there's nothing to check against, and the number comes from your budget alone. The app does the same before payday: until your income is logged, your cash is unknown, not zero.
3. Spread over the days you have left
What's left is divided evenly over the days remaining in your month, today included, and shown for the next seven days. That's a rolling week counted from today, not a countdown to Sunday, so the number doesn't jump on a Monday. In the last days of the month the window shrinks to the days that are left.
per day = left this month ÷ days left
next 7 days = per day × 7 (or × days left, if fewer)
Paid on the 25th? Start your month on the 25th and the days count down to your next payday instead of to the end of the calendar month.
What the app does that this page can't
This page works from one budget total that you type in. In CroSum the same sum runs per category, from the expenses you actually log: groceries, eating out, transport, each with a budget of its own. Recurring bills dated this month count as spent before they go out, and a budget you've set to roll over brings last month's result with it. Overspending in one category comes off the total, so one blown budget can't hide behind the others.
A guideline, not a limit
The number shows what fits your own plan. It isn't permission, and it isn't a spending cap: nothing stops you going past it, and some weeks you'll have a good reason to. It's only as accurate as what you put in. Leave out a bill and it's that much too optimistic.
