About WattlyCalc
WattlyCalc is a small, growing set of free energy cost calculators. Each one answers a single question about what energy costs you, and runs entirely in your browser.
What it is
Energy is one of the few bills that is both large and oddly hard to predict. What does that space heater actually cost? Is it cheaper to charge an electric car at home? Does electric really beat gas for the way you drive? WattlyCalc exists to turn those questions into a clear number in a couple of seconds, with no signup and no spreadsheet.
How it works
Every calculator is plain code that runs inside your own browser. When you move a slider or type a value, the result is computed on your device and shown instantly. Nothing you enter is sent to a server. That keeps the tools fast, private, and free to run.
Each tool follows the same simple layout: a one sentence definition, the calculator itself, a clear breakdown, the exact formula, and a dated worked example so you can check the math yourself. We would rather show our working than ask you to trust a black box.
The numbers we use
Energy cost depends on the price you pay per kilowatt hour, which varies a lot by country, state, and tariff. So every tool lets you set your own rate, with a sensible default preloaded. The default electricity rate reflects the current US residential average reported by the Energy Information Administration. For an exact result, enter the rate from your own bill.
Honest by design
These tools give estimates for general information, not professional or financial advice. We do not invent precision we do not have, and we show the assumptions behind every result. Where a comparison leaves something out, such as the purchase price of a car, we say so on the page.
Who makes it
WattlyCalc is an independent project by Crelvo, a small studio that builds focused web tools. You can see how we handle data in the privacy policy, read the disclaimer, or send a note through the contact page.