get_payment_estimate
Use this to answer 'what would my monthly payment be' for ONE listing. It runs the same itemized out-the-door calculation as estimate_out_the_door (always treated as financed) and turns it into a DEMO monthly finance payment: out-the-door total minus down payment and trade equity, amortized at the APR (or a demo APR by credit_tier) over term_months. Returns finance.estimated_monthly_payment rounded to $5 with monthly_payment_unrounded, monthly_payment_range (rounded outward, so it always contains the unrounded value), financing_eligibility (demo lender rules: minimum amount financed, max term by vehicle age and mileage, with flags), amount_financed_estimate, total_of_payments, finance_charge and every assumption, plus the out-the-door figure it used, a one-line assumptions_summary and any dealer-advertised payment shown separately (not comparable unless the terms match). Totals: total_cost_including_trade_equity (PRIMARY: cash down plus payments plus net trade equity given up) and cash_outlay_excluding_trade_equity (cash down plus payments); total_cost_estimate is a deprecated alias of the latter, kept for one version. For ONE set of terms only: to compare two or more down, term, trade or credit options, call compare_payment_scenarios once instead of calling this tool repeatedly. Use get_price_breakdown instead for the dealer's listed price and fees only, and estimate_out_the_door for the full itemized total without a payment. To find cars by payment across many listings, use search_inventory with max_monthly_payment (canonical; payment_max is a deprecated alias). Estimate, not an offer; dealer sets price, lender sets rate. Not penny-accurate. Leases are not modeled.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| apr | No | APR percent, 0 to 36. If omitted, a demo APR is picked by credit_tier. | |
| payoff | No | Loan payoff owed on the trade-in, USD (negative equity is added to the amount financed). | |
| buyer_zip | No | Buyer's five-digit ZIP. Alone it resolves buyer state, county and city (echoed in tax_location.resolution with the source). | |
| buyer_city | No | Buyer's city, for local tax lines. | |
| listing_id | Yes | dealer_key:VIN from search_inventory. | |
| buyer_state | No | Buyer's two-letter state for tax and fees. Default: the selling store's state, or the state of buyer_zip. | |
| credit_tier | No | excellent, good (default), fair or poor. Picks the demo APR when apr is omitted (used and cpo rates are higher than new). | |
| term_months | No | Loan term in months, 12 to 96. Default 60. | |
| trade_value | No | Trade-in allowance in USD. Passed to the out-the-door step, so it gets the state's trade-in tax credit where allowed. | |
| buyer_county | No | Buyer's county without 'County', for local tax lines. | |
| down_payment | No | Cash down in USD, subtracted from the out-the-door total. Default 0. | |
| trade_equity | No | Net trade equity in USD when allowance and payoff are unknown (negative if upside down). Subtracted after tax, so no trade-in tax credit is applied. | |
| eligible_incentive_labels | No | label_raw values of conditional incentives from get_price_breakdown that the buyer qualifies for. |