# Is It Worth It?

> Buy, rent, repair or subscribe? Compare total cost and NPV over the years you need it. Enter the options you are considering (buy new, rent, repair what you have, subscribe) with upfront, monthly and one-off costs, resale value and a repair allowance. The tool computes total cost of ownership, net present value of costs, cost per month, a ranking and when the best option overtakes the runner-up.

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://isitworthit.usefulweb.site/ (interactive tool at https://isitworthit.usefulweb.site/tool)
- JSON API: POST https://isitworthit.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://isitworthit.usefulweb.site/api/v1/tool)
- OpenAPI: https://isitworthit.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://isitworthit.usefulweb.site/mcp - tool `is_it_worth_it`

## Inputs
- years (integer): How long you need it
- discountRatePercent (number): Discount rate - What money is worth to you per year (e.g. savings interest). Used for NPV only.
- currency (text): Currency - Shown in results only; no conversion is performed.
- options (table, required): Options - Costs are positive numbers. Resale is what you expect to get back at the end. One-off year 0 = at the start.

## Method
- Annual running cost = recurring per month × 12 + repair allowance per year.
- Total cost (nominal) = upfront + one-off costs + years × annual running cost − resale value.
- NPV cost = upfront + one-off ÷ (1 + r)^y + Σ(t = 1..N) annual running cost ÷ (1 + r)^t − resale ÷ (1 + r)^N, where r = discount rate and y = the one-off year (running costs are discounted at each year end).
- Cost per month = total cost ÷ (12 × years); NPV cost per month = NPV cost ÷ (12 × years).
- Options are ranked by NPV cost (lowest first); ties keep input order.
- Break-even: nominal cumulative costs of the best and runner-up options are compared at each year end (resale counted only at the end, one-off costs from their year) and the crossing point is interpolated linearly.