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

    Frequently Asked Questions

    Do I need 20% down?

    No, many loans require as little as 3-5% down. However, putting less than 20% down typically requires PMI, adding $50-200/month.

    Learn More

    Guide

    How to Calculate Mortgage Payments

    Learn how to calculate mortgage payments step by step. Understand the mortgage payment formula, principal vs. interest breakdown, escrow, PMI, and how to use amortization schedules.

    Ready to run the numbers?

    Open Down Payment Calculator