About InstaCalcs
InstaCalcs is a collection of calculators for the small but annoying math that comes up all the time: mortgage payments, tax estimates, BMI, calories, loan payments, tips, timestamps, and plenty of other bits.
Why this exists
Most online calculators make you work too hard before you get the answer. Some bury the result under ads. Some ask for an account. Some hide the formula entirely. InstaCalcs tries to keep the useful part front and center: the inputs, the result, the formula, and the caveats.
What you can calculate
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Finance Tools
Mortgage payments, compound interest, tax estimates, student loans, and payoff timelines.
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Health Tools
BMI, daily calories, body fat estimates, water intake, due dates, and training zones.
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Utility Tools
Word counts, JSON formatting, passwords, colors, units, Base64, and timestamps.
What happens to your numbers
Calculator inputs run in your browser whenever possible. We do not store the salary you typed in, your loan balance, your body measurements, or the date you entered into a pregnancy calculator.
Who maintains it
InstaCalcs is maintained as an independent calculator project. Updates come from bug reports, user suggestions, source changes, and routine checks against public references such as the IRS, Social Security Administration, Consumer Financial Protection Bureau, CDC, and Investor.gov.
How calculators are built
Each calculator starts with a formula and a short list of assumptions. Then we check the examples by hand. For finance and tax pages, that usually means comparing thresholds or formulas against sources such as the IRS, Social Security Administration, CFPB, or Investor.gov. For health pages, it means citing public health guidance where we can and being clear that the result is an estimate.
Some subjects are messier than the formula makes them look. Taxes depend on deductions and local rules. Health numbers vary from person to person. A mortgage payment can change once you add insurance, taxes, and HOA fees. The calculators should help you understand the ballpark, not pretend the ballpark is the whole map.
How we check the work
The review process is boring on purpose:
Known results. Calculator formulas are checked against hand calculations, published examples, and public reference calculators where they exist. The mortgage calculator follows the standard fixed-rate amortization formula. The BMI calculator uses CDC formulas and adult categories. The compound interest calculator follows the same core compounding model used by Investor.gov.
Visible sources. Priority calculators list the sources used to check the formula or assumptions. If a formula has several common versions, the page should say which one it uses.
Updates when the facts change. Tax brackets change. Social Security wage bases change. Health guidance can shift. Pages that depend on those details need review dates because stale math is worse than no math.
How articles are edited
Articles should explain the math like a person would: enough context to understand the result, enough examples to check it, and enough caveats to avoid overtrusting it.
Sources where they matter. Tax, finance, and health claims should point back to public sources when possible.
Examples you can check. A guide is more useful when it says, "A $300,000 mortgage at 6.5% over 30 years is about $1,896 a month," than when it talks vaguely about planning ahead.
Plain caveats. Calculators are helpful, but they are not financial, medical, or tax advice. The site should say that clearly without turning every page into legal fog.
Get in touch
Found a bug, spotted a stale number, or want a calculator that is missing? Send it through the contact page.