Down Payment Calculator Formula

Understand the math behind the down payment calculator. Each variable explained with a worked example.

Use the Down Payment Calculator

Formulas Used

Down Payment Needed

down_payment_out = down_payment

Still Need to Save

remaining_out = remaining > 0 ? remaining : 0

Months to Save

months_to_save = monthly_savings > 0 ? (remaining > 0 ? ceil(remaining / monthly_savings) : 0) : 0

Resulting Loan Amount

loan_amount = home_price - down_payment

Variables

VariableDescriptionDefault
home_priceHome Price(USD)350000
down_percentDown Payment Percentage(%)20
current_savingsCurrent Savings(USD)30000
monthly_savingsMonthly Savings(USD)1000
down_paymentDerived value= home_price * down_percent / 100calculated
remainingDerived value= down_payment - current_savingscalculated

How It Works

Down Payment Calculation

Down Payment = Home Price × Down Payment%

Months to Save = (Down Payment - Current Savings) / Monthly Savings

Common Down Payment Amounts

  • 20% — Avoids PMI (private mortgage insurance)
  • 10% — Common conventional minimum
  • 3.5% — FHA minimum
  • 0% — VA loans (eligible veterans)

    • Worked Example

    $350,000 home with 20% down, $30,000 saved, saving $1,000/month.

    home_price = 350000down_percent = 20current_savings = 30000monthly_savings = 1000
    1. 01Down payment = $350,000 × 20% = $70,000
    2. 02Still need = $70,000 - $30,000 = $40,000
    3. 03Months to save = $40,000 / $1,000 = 40 months
    4. 04Loan amount = $350,000 - $70,000 = $280,000

    Ready to run the numbers?

    Open Down Payment Calculator