The Car Lease vs. Buy Financial Decision Engine compares total five-year net financial outlays between auto loan financing and vehicle leasing to determine which option saves money.

### Core Comparison Mechanics Comparing lease versus purchase options requires looking past the monthly payment to examine true retained equity at the end of the term: - **Loan Financing (Purchase)**: - Down payment plus loan principal and interest over the loan term (e.g. 60 months). - Monthly payment: $\text{Payment} = P \times \frac{r(1+r)^n}{(1+r)^n - 1}$ - **Net Purchase Cost**: Total loan outflow minus end-of-term vehicle residual market value ($\text{Outflow} - \text{Residual Equity}$). - **Vehicle Leasing**: - Down payment plus continuous monthly lease payments over 60 months ($5\text{ years}$): $\text{Total Outlay} = \text{Down} + (\text{Monthly Lease} \times 60)$. - Zero asset equity retained at the conclusion of the lease period unless purchased via contractual buyout.

### Worked Financial Comparison Using standard vehicle purchase benchmarks: - **Agreed Vehicle Price**: $42{,}000 - **Down Payment**: $4{,}000 (Loan Principal: $38{,}000) - **Auto Loan**: 60 months at $6.0\% \implies \approx $734.68\text{/month}$ - **Total Purchase Outflow**: $4{,}000 + ($734.68 \times 60) = $48{,}081 - **Net Buy Cost (after $18{,}000 residual)**: $48{,}081 - $18{,}000 = $30{,}081 - **Lease Outflow ($480/mo for 60 mos)**: $4{,}000 + ($480 \times 60) = $32{,}800 - **Financial Verdict**: **Buying saves $2{,}719** over 5 years because you retain the vehicle's resale value.

### Local Client-Side Financial Modeling All loan amortizations, interest schedules, and financial verdicts calculate strictly inside your local browser runtime. No vehicle budgets, loan terms, or credit parameters are uploaded to any server.