Car lease calculator

A lease term that is not a positive integer fails with invalid_input instead of being truncated.

What a car lease payment is and how the two-part formula works

The response also reports depreciation and finance_fee separately so a shopper can see how much of the payment is using up the car versus paying for the use of money, and it reports total_of_payments as the monthly figure times the term. Acquisition fees, documentation charges, and sales tax are not invented: add them to negotiated_price if they are capitalized into the lease, otherwise leave them out of this pretax identity.

Input contract, response shape, and error behaviour

Lease term is the field the product contract singles out: it must be a whole number of months, never a year count silently multiplied, never a rounded decimal. POST a JSON body with four required fields: negotiated_price, the capitalized selling price as a finite number at least zero (aliases price, cap_cost, capitalized_cost, and selling_price); residual_value, the contract residual in currency as a finite number at least zero, not a percent of sticker (aliases residual and residual_amount); money_factor, the dealer money factor as a finite number from zero through one, for example 0.00125 rather than three for three percent APR (aliases mf and factor); and lease_term, the term as a positive integer number of months from one through one hundred twenty (aliases term, months, and term_months). Each numeric field may arrive as a JSON number or as a numeric string. Missing fields, empty strings, non-finite values, a negative price or residual, a money factor above one, and any lease_term that is not a positive integer—zero, a fraction such as thirty-six point five, a boolean, or a non-numeric string—fail with invalid_input naming the field and are not billed. On success the body echoes negotiated_price, residual_value, money_factor, and lease_term, and adds depreciation, finance_fee, monthly_payment, total_of_payments, and a formula string restating the two-part identity. Example: negotiated_price thirty-five thousand, residual_value twenty thousand, money_factor 0.00125, lease_term thirty-six yields depreciation of the fifteen-thousand gap over thirty-six months plus a rent charge of fifty-five thousand times the factor, rounded to two decimals. Pair the figure with your own tax table if the jurisdiction taxes the payment; this endpoint computes pretax lease math only.

Where a car lease calculator earns its keep

Failed validation does not consume balance. Quote tools and comparison pages can call the same pure module from the browser for free previews and from the API when storing a scenario, guaranteeing that the payment a visitor saw on a landing page matches the payment stored after they save a quote. Personal-finance apps and household budgets already know a down payment or trade-in; subtracting those credits from the selling price and posting negotiated_price, residual_value, money_factor, and lease_term fills a card with monthly payment, depreciation, finance fee, and total of payments so a driver can see whether thirty-six months is cheaper in cash than twenty-four at a higher monthly hit. Educators teaching lease versus loan math can seed classroom examples that fail loudly when lease_term is not a positive integer, instead of silently truncating 36.7 months into thirty-six. Content teams can illustrate zero-factor promotions with money_factor zero, where the payment collapses to depreciation without a hidden rent charge. Keep lease_term a whole number of months, pin the rounded money fields in tests, and you get reproducible car lease payments for widgets, LMS modules, and edge workers without a lending stack of your own.