What a monthly budget hides

Every budgeting tool I have used shows you a month. Income at the top, expenses underneath, what is left over at the bottom. If that last number is positive you are fine.

Except money does not leave your account when you spend it.

A card purchase on the third leaves the bank on the twenty-second of the following month, or whenever that card’s statement happens to cycle. A second card cycles on a different day. Some expenses cannot go on a card at all and come straight out of checking. So the thing your budget calls “March expenses” is actually a scattering of withdrawals across March, April and May, in an order nobody chose and the budget never shows you.

The budget says you are fine for the month. The account is short on the eleventh.

You can avoid the whole problem by not using credit cards, and some well-known financial advisors tell you to do exactly that. It is not terrible advice. I do believe I would spend less overall without them.

But there is cash back, and there is the part that actually matters: when a charge is wrong, I dispute it and the bank sorts it out while the money is still theirs. Nobody has reached into my checking account in the meantime. That is worth real money to me, more than the cash back is, and I travel for work often enough to use it.

So I keep the cards and live with the float.

The budget is a model

The float is the obvious failure. The deeper one took me longer to see.

A budget is a model. Categories, targets, a number you hit or miss. You can hit it every month for a year and still have less money than you started with, because the model left something out. An annual expense that did not fall in any month you were looking at. A category you quietly revised upward. The float again.

The bank balance does not have that problem. It is not a model of anything. It is the number, and across a year it is either higher than it was or it is not.

So that became the measure. Not whether I hit a budget, but whether the balances are up. If they are not, the budget was telling me something untrue, and it does not matter how disciplined I was about it.

Which is why I built the thing

Runway forecasts the balance, daily, account by account, with the float modeled rather than averaged away. It leads with the lowest point it can see, the day it happens, and how far under the floor it goes.

Because it models the cards, it also tells me what the next statement is going to be, days before the statement exists. That turned out to be the useful part. Discretionary spending on a card is invisible until the bill arrives, and by then it is a fact. Watching the number build while I can still do something about it has done more for my finances than any budget I have kept.

It changed how I hold money too. The lumpy costs are the ones that hurt: a tax bill, a tuition payment, something that lands once a year and swamps the month it falls in. I now keep separate accounts for those and fund them a little at a time. Account by account, the forecast shows each one filling up against the date it is needed.

That is the part I did not expect. Watching a forecast climb is a different experience from watching a category stay under its cap. One is reassurance. The other is compliance. I know the big payments are covered because I can see them being covered, months out, and I have not had that before.

Runway has been a personal project, built entirely for me and my household. If you would find it useful too, let me know.