# True Cost Calculator

> What a car, pet, appliance, home or gadget really costs per year, month and day. Add the purchase price, financing, expected resale value, recurring costs, maintenance, insurance and energy use. The calculator returns the true total cost of ownership, the cost per year, month and day, the share of each cost bucket, and how many times the sticker price you really pay.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://truecostcalculator.usefulweb.site/ (interactive tool at https://truecostcalculator.usefulweb.site/tool)
- JSON API: POST https://truecostcalculator.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://truecostcalculator.usefulweb.site/api/v1/tool)
- OpenAPI: https://truecostcalculator.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://truecostcalculator.usefulweb.site/mcp - tool `true_cost_calculator`

## Inputs
- itemType (select): What is it?
- itemName (text): Name
- currency (text): Currency - Shown in results only; no conversion is performed.
- purchasePrice (number, required): Purchase (sticker) price
- yearsOwned (number): Years you will own it
- resaleValue (number): Expected resale value at the end
- loanAmount (number): Loan amount - Leave 0 if you pay cash.
- aprPercent (number): Loan APR
- loanTermMonths (integer): Loan term
- maintenancePerYear (number): Maintenance / repairs per year
- insurancePerYear (number): Insurance per year
- energyConsumption (number): Energy / fuel consumption - E.g. 6 (litres per 100 km) or 150 (kWh per year of use = 1 usage unit).
- consumptionPer (select): Consumption is per
- energyUnitPrice (number): Price per energy unit - E.g. price per litre or per kWh.
- usagePerYear (number): Usage per year - E.g. km per year, wash cycles per year.
- recurring (table): Other recurring costs - Taxes, parking, food, subscriptions, fees…

## Method
- Depreciation = purchase price − expected resale value (the money you will not get back).
- Loan interest is computed from an exact monthly annuity schedule: payment = L·i ÷ (1 − (1 + i)^−n) with i = APR ÷ 12 and n = term in months; only interest falling within the ownership period (years × 12 months) is counted.
- Recurring costs are annualised: weekly × 365.25/7, monthly × 12, quarterly × 4, yearly × 1; then multiplied by years owned.
- Energy per year = consumption ÷ (1 or 100) × usage per year × price per energy unit.
- True total = depreciation + loan interest + years × (recurring + maintenance + insurance + energy per year).
- Per year = total ÷ years; per month = total ÷ (12 × years); per day = total ÷ (365.25 × years). Sticker multiplier = total ÷ purchase price.