Cash Flow Calculator
Model your next 12 months of cash and find the exact month your balance bottoms out — the negative-month trough that single-number tools miss.
Written by Dorothy Ibrahim, 10+ years in banking & finance
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How we calculate this
This calculator rolls your cash balance forward month by month for a full year and flags the exact month it bottoms out — including any months it goes below zero. Profitable businesses still fail when the timing of cash in and cash out leaves a gap, and a single-number cash figure hides that trough. Knowing the low month, and how deep it goes, tells you how early you need financing, faster collections, or cost cuts.
The formulas
- Closing cash for a month
- opening cash + inflows for the month − outflows for the monthOne-time items are added to their month’s inflow or outflow total before this step.
- Next month’s opening cash
- this month’s closing cash
- Lowest cash point
- the smallest closing balance across the 12 months
- Months below zero
- count of months whose closing balance is negative
- Average monthly outflow
- total outflows across 12 months ÷ 12Used for the "thin cushion" check: a low point under one month of average outflows draws a caution.
Worked example
- Say you start with $30,000 of cash, and every month brings in $20,000 and pays out $22,000.
- Each month the balance drifts down by $22,000 − $20,000 = $2,000: month 1 closes at $28,000, month 2 at $26,000, and so on.
- By month 12 the closing balance is $30,000 − (12 × $2,000) = $6,000 — that is both the ending cash and the lowest point of the year.
- No month closes below zero, so months below zero is 0.
- Average monthly outflow is $22,000, and the $6,000 low point is well under one month of outflows — the tool flags a thin cushion, because a single late payment could tip you negative.
Rates, benchmarks & sources
- "Thin cushion" threshold — a cash low point below one month of average outflows — is a working-capital heuristic, not a lender standard. — Industry rule of thumb
- Rolling cash model: closing = opening + inflows − outflows, carried month to month. — Standard cash-budgeting arithmetic
Figures current as of 2026-07-02. See our methodology & editorial standards for how constants are versioned and verified.
What this tool doesn’t model
- It models the timing you enter, not the timing you will get — if a customer pays 30 days late, your real trough is deeper than the model shows.
- Monthly buckets hide intra-month swings: rent due on the 1st before a mid-month receivable can create a shortfall the month-end balance never reveals.
- It is a cash model, not a profit model — it says nothing about margins, and it ignores accrual items like depreciation or unbilled work.
- Negative monthly inflow or outflow entries are treated as zero; refunds and other reversals must be entered as one-time items in the opposite direction.
Frequently asked questions
Why does the lowest cash point matter more than my ending cash?
A year that ends with a healthy balance can still pass through a month where you cannot make payroll. The trough is where the business actually breaks, and financing takes time to arrange — so the month it happens, not the December number, sets your deadline for action.
What should I do if the calculator shows a negative month?
A negative month means that, on your current plan, you run out of cash before the year ends. The options are the same three levers every time: bring cash in sooner (collections, deposits, invoicing faster), push cash out later (negotiating terms with vendors), or bridge the gap with financing arranged before the trough. The AR Aging and Line of Credit calculators on this site look at the first and third levers.
How do I use the one-time items instead of editing the monthly grid?
The monthly grid is for your recurring pattern; one-time items are for events that hit a single month — a tax payment, an equipment purchase, an insurance refund, a seasonal inventory buy. The tool folds each item into that month’s inflow or outflow total, which keeps your recurring baseline clean and makes the item easy to remove later.
My business never goes negative — why does the tool still show a caution?
The caution fires when your lowest balance is under one month of average outflows. That is an industry rule of thumb, not a regulation: with that thin a cushion, one late-paying customer or one surprise expense can push you below zero, so the tool flags it even though the modeled curve stays positive.
Should the inflows be my revenue or my collections?
Collections — cash that actually lands in the bank that month. If you invoice on net-30 terms, revenue booked in March is usually cash in April or later, and entering revenue instead of collections will make every month look better than it is. The same logic applies to outflows: enter when you pay, not when you are billed.
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themoneysheet provides educational estimates, not financial, tax, or legal advice. Figures use published rates and formulas current as of the date shown, but your situation may differ. Consult a qualified professional (CPA, attorney, or licensed advisor) before making financial decisions.