Cash Flow Projection Calculator

Method & sources

This calculator is educational, not advice. It projects closing cash from the flat monthly figures you enter; it is not a forecast, and not financial, accounting, tax or legal advice. For decisions about funding, borrowing or spending, check your own detailed projection with a qualified accountant or adviser.

Formula

Net per month = Cash in per month - Cash out per month. The same two figures are used for every month: there is no growth rate, no seasonality and no month-by-month schedule.

Closing cash = Opening cash + Net per month x Months to project. Because every month is identical, this single multiplication gives the same answer as carrying each month's ending cash forward as the next month's starting cash.

If closing cash is below zero, the result adds a warning that the balance goes negative, meaning the money runs out before the end of the period. The tool does not stop the projection at zero: it keeps subtracting and shows the negative figure.

Only when Net per month is below zero, the tool also shows Cash runs out after = Opening cash / (Cash out per month - Cash in per month) months. This is worked out from the opening cash and net figure alone, so it can be longer than the months you asked it to project.

Alongside that, 'Which is around, if the projection starts today' shows a calendar month: today's date in your browser moved forward by the runway converted to days (months x 30.4375, the average month length, rounded to the nearest whole day), shown as month and year. Part months count, so a 3.3-month runway lands about 101 days ahead.

If Net per month is zero or positive, no runway or date is shown.

Rounding

Money figures are shown to the nearest cent for display only, formatted by your browser's locale; negative amounts appear with the minus sign before the dollar sign, as -$52,000.00. The runway is shown to one decimal place (toFixed(1)). For the calendar month, the unrounded runway is converted to days at 30.4375 days a month and rounded to the nearest whole day. Nothing is rounded before the arithmetic.

Inputs used

• Opening cash (required, 0 or more)
• Cash in per month (required, 0 or more; applied unchanged to every month)
• Cash out per month (required, 0 or more; applied unchanged to every month)
• Months to project (required, 1 to 60; decimals are accepted and used as entered)

What this does not account for

• Growth or decline in sales or costs: in and out are flat for the whole period
• Seasonality, lumpy bills and the timing of individual payments within or across months
• Customer payment terms (money owed to you but not yet received) and supplier payment terms
• One-off items such as equipment purchases, loan proceeds, loan repayments, owner draws or new investment, unless you fold them into the monthly averages yourself
• Taxes, interest earned on cash, and inflation
• A negative opening balance or an overdraft or credit line: opening cash cannot be below zero and no borrowing is modelled when cash runs out

Jurisdiction

Not jurisdiction-specific. It is plain arithmetic on figures you enter and embeds no tax rate, threshold or benchmark. Figures display with a dollar sign, but any single currency works if used consistently.

Source

FDIC and U.S. Small Business Administration, Money Smart for Small Business, Module 10: Managing Cash Flow (Participant Guide, FDIC-029-2025)

Effective date

Not date-sensitive: starting cash plus inflows minus outflows equals ending cash is a stable accounting identity, not a value that changes on a schedule.

Version

1.1

Last substantive review

2026-09-23

Limitations

• The FDIC/SBA guide defines net cash flow as the difference between total cash inflows and outflows over a period, and its worked six-month projection carries each month's ending cash forward as the next month's starting cash. It does not give the closing-cash or runway formula above as an equation; those are the direct arithmetic of that definition under the tool's flat-monthly assumption, verified against this tool's own code.
• The source's projections vary month by month and separate operating, investing and financing activities. This tool collapses all of that into one average in and one average out, so it is the simplest possible projection, not a full pro-forma cash flow statement.
• The runway and its calendar month assume money leaves evenly through each month and that the projection starts today. The month is worked out with an average month length (30.4375 days), not your actual calendar, so it is approximate: when the runway ends near a month boundary, the month shown can be one either side of the real one.
• If opening cash is 0 and net is negative, the runway shows 0.0 months and the current month.
• This is a planning estimate from your own averages, not a forecast of what your business will do.

Reference cases

Five worked examples you can check by hand against the formula above.

Change log