THE NUMORIX GUIDE
How to use the Cash Flow Calculator
Last reviewed September 14, 2026
What this calculator does
The engine scales monthly income, expenses, and investments by the entered number of months.
Formula and method
The engine scales monthly income, expenses, and investments by the entered number of months. Ending cash equals beginning cash plus total income minus total expenses and investments. Net cash flow excludes beginning cash, while savings rate is (total income - total expenses) / total income and therefore does not subtract the investments field.
Variables and inputs
Enter beginning cash, monthly income, monthly expenses, monthly investments, and period in months. All monetary inputs are dollars; months is the projection count.
Worked example
With $10,000 beginning cash, $5,000 monthly income, $3,500 monthly expenses, $500 monthly investments, and 12 months, income is 5,000 x 12 = $60,000, expenses are $42,000, and investments are $6,000. Ending cash is 10,000 + 60,000 - 42,000 - 6,000 = $22,000; net cash flow is $12,000.
How to interpret the result
Ending cash includes the opening balance, while net cash flow measures the period's change before adding that opening balance. The savings-rate output describes income left after expenses under the engine's definition, so compare it with investment contributions separately.
Common mistakes to avoid
Do not enter annual totals in monthly fields. Do not add beginning cash to net cash flow. Notice that investments reduce ending cash but are not subtracted in the displayed savings-rate formula.
Assumptions and limitations
The model uses level monthly amounts and no return on cash or investments. It excludes timing within a month, taxes, debt principal, irregular bills, investment gains, inflation, and overdraft constraints. It does not distinguish cash from invested assets in ending cash.
Practical use and checks
Use the Cash Flow Calculator to see how recurring monthly income, expenses, and investments change cash over a selected number of months. It is especially helpful for testing whether a planned transfer to savings is sustainable after bills. For a check, enter $10,000 beginning cash, $5,000 monthly income, $3,500 monthly expenses, $500 monthly investments, and 12 months. Total income should be $60,000, total expenses $42,000, total investments $6,000, and ending cash $22,000. The net cash flow is $12,000 because investments are treated as money leaving cash, while the displayed savings rate is 30%, calculated from income minus expenses before investments. Read the ending balance as a bookkeeping projection, not as proof that the money will be available on every date. A positive twelve-month total can conceal a short-term overdraft if income arrives after rent or debt payments. The calculator assumes the same amount repeats each month and does not model interest, taxes, irregular bills, debt payments as a separate category, inflation, investment returns, transfers between accounts, or the timing of paydays. Negative ending cash is a useful warning to revise the plan, but it is not a bank overdraft forecast. For a major decision, add a month-by-month calendar for variable bills and maintain a separate emergency-fund target.