About CheckPre: how the calculators are built
CheckPre has 437 free calculators across 16 categories, from EMI and income tax to LLM API spend, cloud egress, shipping DIM weight and rooftop solar, each with its formula, a worked example and, where rules or prices are involved, its sources. There is no sign-up, no paywall and no limit on how often you use them.
Why every page shows its formula
A number on its own is hard to trust. Every calculator here sets out the formula it uses, defines each term, and walks through a worked example with real figures, so you can check the result by hand if you want to or follow the same method somewhere else.
How the calculations are checked
The arithmetic lives in plain functions that are covered by automated tests. The loan schedule is verified to repay exactly the amount borrowed and close at a zero balance, and the EMI formula is cross-checked against a month-by-month simulation that uses no formula at all. Conversions use the internationally agreed exact factors rather than rounded ones.
What these results are not
They are estimates, not advice. A loan calculation cannot know your lender's processing fees or insurance charges; an investment projection assumes a steady return that no real fund delivers; and a health figure is a screening estimate, not a diagnosis. Check anything that matters with your bank, your adviser or your doctor before acting on it.
Everything runs in your browser
Every calculation happens on your own device, which is why the results update as you type and why there is no account to create. The one exception is the snow day calculator, which sends the place you type to this site's server to look up the forecast; see the privacy page.