How do you calculate safe to spend?

Take the income for the month, subtract the fixed costs that have not been paid yet, subtract the savings you promised yourself, subtract what you have already spent, then divide what is left by the days remaining. The result is what one more day can cost without breaking the plan.

Why divide by days instead of just looking at the balance?

Because a balance flatters you. A bank balance on the eighth of the month looks generous precisely because the rent has not left yet, and a daily figure is the only version of the number that accounts for the days still to come.

Is this the same as the app figure?

It is the same arithmetic. The difference is that the app already knows what you have spent, because you have been entering it as you go, so it can keep the number current without you retyping four fields.

What should I do when the number goes negative?

Read it as early warning rather than as a verdict. A negative figure on the twelfth is recoverable and worth a decision now: which envelope absorbs it, or does the savings promise move this month. Deciding deliberately is the difference between an adjustment and a spiral.

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Safe to spend today

Bank balances lie by omission: they show the rent you have not paid yet as though it were yours. This is the honest version, per day, for the days that are left.

The daily allowanceWhat today can cost

$78.57

a day for the 14 days that are left, from $1,100 still uncommitted.

What a bank balance leaves outThe subtraction, in full

Income this month$4,000
Fixed costs still to pay$1,600
The savings promise$600
Spent so far$700
Uncommitted, for the rest of the month$1,100

The days still to pay for14 days at $78.57

Each remaining day carries the same figure, which is what a balance never tells you: the rent that has not left yet is not yours to spend.

Committed or already spent this month: $2,900
Share of income still unspent: 28%
A day, if today costs nothing: $84.62

A workable daily figure. Check it before the spend rather than after, because after is just accounting.

$1,100 still uncommitted this month$550 over the next week, at this rate14 days still to pay for

Set the promise this figure is built on →

The number for 4pm on a ThursdayDaily, because months are decided daily

01Why daily

Nobody weighs a purchase against a monthly allocation.

Why the daily number is the one that changes behaviour

Monthly budgets are decided daily. Nobody stands in a shop weighing a purchase against a monthly allocation, because the comparison is too abstract to make in the time available. A daily figure is the right size for that moment: it is small, it is concrete, and it is obviously spent or not spent by the end of the day.

It also makes the middle of the month visible. Most overspending is not one dramatic purchase, it is a run of ordinary days that each looked affordable in isolation. Dividing by the days remaining is what turns that run into something you can see while it is happening.

02In the method

Where it sits in the method

Kakeibo asks four questions once a month. Safe to spend is the daily instrument between two of them: you have already answered how much you have and how much you promised to save, and this keeps the third question, how much you are spending, in front of you while the month is still running.

To set the promise in the first place, use the kakeibo calculator, and to check how a target lands over months rather than days, the savings target calculator does the horizon arithmetic.

03The limitation

It knows exactly as much as you typed into it.

The honest limitation

This calculator only knows what you type into it, which means it is accurate for about as long as your memory of what you have spent. That is the whole argument for writing entries down as they happen rather than reconstructing them, and it is the reason kakeibo has always been a pen and paper practice first.

Common questions

How do you calculate safe to spend?: Take the income for the month, subtract the fixed costs that have not been paid yet, subtract the savings you promised yourself, subtract what you have already spent, then divide what is left by the days remaining. The result is what one more day can cost without breaking the plan.
Why divide by days instead of just looking at the balance?: Because a balance flatters you. A bank balance on the eighth of the month looks generous precisely because the rent has not left yet, and a daily figure is the only version of the number that accounts for the days still to come.
Is this the same as the app figure?: It is the same arithmetic. The difference is that the app already knows what you have spent, because you have been entering it as you go, so it can keep the number current without you retyping four fields.
What should I do when the number goes negative?: Read it as early warning rather than as a verdict. A negative figure on the twelfth is recoverable and worth a decision now: which envelope absorbs it, or does the savings promise move this month. Deciding deliberately is the difference between an adjustment and a spiral.

The rest of the setEach figure is that tool's own opening answer

How do I split my income the kakeibo way?Kakeibo calculator$1,500left to divide, on a 4,000 monthOpen it →What does my goal cost per month, week and day?Savings target calculator$833a month, for 10,000 in a yearOpen it →What shape did my month actually have?Four category split$600left over, on that month as spentOpen it →Which allocation suits my income better?Kakeibo vs 50/30/20$800is what the rule would ask forOpen it →Am I doing better than last month?Savings rate15%saved, 2.5 months coveredOpen it →All of them, with a preview of each answerThe calculator hub家計簿Every instrument on this siteOpen the hub →

One number, checked before you spend

It is a small habit with a disproportionate effect, and it is the reason the app puts this figure on the home screen rather than three screens deep.

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The Kakeibo app home screen showing net worth, accounts and the month's progress