THE NUMORIX GUIDE
How to use the Down Payment Calculator
Last reviewed September 14, 2026
What this calculator does
The route calculates down payment as home price x down-payment percent and the financed amount as the remainder.
Formula and method
The route calculates down payment as home price x down-payment percent and the financed amount as the remainder. It uses a fixed-rate mortgage formula for principal and interest. To estimate saving time, it starts with zero saved, credits the monthly savings return to the accumulated amount, adds the monthly savings, and repeats until the target down payment is reached or 600 months pass.
Variables and inputs
Enter home price, down payment percent, mortgage rate, loan term of 15 or 30 years, monthly savings, and savings return. Home and savings values are dollars; down payment and rates are percentages; the savings horizon is monthly.
Worked example
For a $350,000 home and 20% down, the required down payment is 350,000 x 0.20 = $70,000 and the loan is $280,000. At 6.5% over 30 years, monthly principal and interest is about $1,769. If savings return is 4%, the first month of a $500 plan grows from zero to $500 because the first balance has no interest; the next month starts with 500 x (1 + 0.04 / 12) + 500 = $1,001.67.
How to interpret the result
The route combines an upfront purchase scenario with a separate accumulation estimate. It does not say that the displayed down payment is the only cash needed to buy. Closing costs, reserves, insurance, taxes, and loan-program minimums may require additional funds.
Common mistakes to avoid
Enter 20 for 20%, not 0.20. Keep monthly savings separate from the savings return percentage. Do not subtract the down payment from the home price twice when interpreting the loan amount.
Assumptions and limitations
The saving loop starts at zero and stops at 600 months, and it does not include existing savings, taxes, fees, or changes in home price. The mortgage payment excludes mortgage insurance, property tax, and homeowners insurance.