# 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.app (https://usefulweb.app/). 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.app/ (interactive tool at https://truecostcalculator.usefulweb.app/tool)
- JSON API: POST https://truecostcalculator.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://truecostcalculator.usefulweb.app/api/v1/tool)
- OpenAPI: https://truecostcalculator.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://truecostcalculator.usefulweb.app/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 - Pet: purchase or adoption fee.
- 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 or vet care per year - Car or appliance: servicing and repairs. Pet: vet visits, vaccinations, medication and other health care.
- insurancePerYear (number): Insurance per year - Pet: health or liability insurance.
- energyConsumption (number): Energy, fuel or food consumption - Car: e.g. 6 (litres per 100 km). Appliance: e.g. 1.2 (kWh per wash cycle). Pet: e.g. 0.35 (kg of food per day).
- consumptionPer (select): Consumption is per
- energyUnitPrice (number): Price per unit (litre, kWh or kg of food) - E.g. price per litre of fuel, per kWh or per kg of pet food.
- usagePerYear (number): Usage per year - E.g. km per year, wash cycles per year, or 365 feeding days for a pet.
- recurring (table): Other recurring costs - Taxes, parking, subscriptions, pet supplies, grooming, 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, fuel or food per year = consumption ÷ (1 or 100) × usage per year × price per unit.
- True total = depreciation + loan interest + years × (recurring + maintenance or vet care + insurance + energy, fuel or food per year).
- Per year = total ÷ years; per month = total ÷ (12 × years); per day = total ÷ (365.25 × years). Sticker multiplier = total ÷ purchase price.