THE NUMORIX GUIDE
How to use the Savings Calculator
Last reviewed September 14, 2026
What this calculator does
The projection starts with the initial deposit and advances through the selected number of periods per year.
Formula and method
The projection starts with the initial deposit and advances through the selected number of periods per year. Each period adds the monthly contribution converted to that frequency, then credits balance x (annual rate / periods). At each year end it subtracts taxRate percent of that year's interest, reports purchasing power as balance divided by (1 + inflation)^year, and increases the next year's monthly contribution by annualContributionGrowth.
Variables and inputs
Enter initial deposit, monthly contribution, annual contribution growth, years, annual interest rate, compound frequency of 1, 2, 4, 12, or 365, tax rate, and inflation rate. Money inputs are dollars; years is a whole projection count; rates are annual percentages.
Worked example
With a $10,000 initial deposit, $500 monthly contribution, 4% annual rate, monthly compounding, and no tax, the first period adds $500 to make $10,500 and credits 10,500 x (0.04 / 12) = $35.00, leaving $10,535.00. Over 12 months the contributions are $6,000, before the next year's contribution growth is applied.
How to interpret the result
The final balance combines deposits and modeled interest after the annual tax deduction. Purchasing power is expressed in the starting price level using the entered constant inflation rate. A daily setting changes the number of periods and the contribution conversion, so compare frequency choices with the same other assumptions.
Common mistakes to avoid
Enter contribution growth as a percentage such as 3, not 0.03. Do not treat the tax field as a withholding percentage on every deposit. Confirm that the selected compounding frequency is supported by the account rather than assuming daily compounding from a quoted annual rate.
Assumptions and limitations
The engine applies tax once per year to modeled interest, assumes contributions are evenly spread within each selected frequency, and uses a constant return and inflation rate. It does not include account fees, contribution limits, changing rates, withdrawal penalties, or investment losses.