Why this site exists
Search for a calculator and you'll usually land on a page buried in ads, with a form that wants your email before it gives you a number. Or the tool is fine but the math is wrong, and nobody says how it was worked out.
OnSumo started as a fix for that. Small tools, honest math, no gates. The goal is simple: you open a page, you get your answer, you leave.
How a tool gets built
Each tool starts with a real question people ask. We find the standard formula, write it down in plain code, and test it against worked examples from textbooks, official guidance or hand calculations. If the example doesn't match, the tool doesn't ship.
Rates, fee tables and tax brackets sit in dated data files. That lets us show which year a figure comes from and update it in one place. Every page also lists its limits, because every calculator has some.
What we don't do
The same inputs give the same output every time. That's a feature. You can check it, repeat it and trust it.
- Ask you to sign up or give an email
- Use AI to generate your result
- Sell your inputs, since most tools never send them anywhere
- Pretend an estimate is professional advice
How it's paid for
Hosting costs money and so does the time to build and check tools. The site is supported by ads, which is why you'll see some. We try to keep them out of the way of the tool itself. If an ad ever blocks a result or makes a page hard to use, tell us.
Who's behind it
An independent developer who works with automation, SaaS products and technical SEO. That background shows up in the tool list, which leans toward builders, freelancers and small business owners, alongside everyday money and health questions.
Mistakes happen. If you find one, write to us. We'd rather fix a wrong number than defend it. Corrections get checked against the source, then updated in the data and in the guide that explains it.
Where to start
Browse the categories on the tools page, or open a Learn guide if you want the formula before the calculator. Bookmark the ones you use. The URLs don't change.
How a tool gets built
It usually starts with a question people keep asking. How much does a patent really cost? What does a three-month freelance gap do to my rate? Is a 60,000 mile ticket a good deal? We look for the formula or the rule behind it, find the source and write the calculator.
Then we test it with numbers we can check by hand. If the answer differs from a worked example in an official guide, we fix it before publishing. After release, the page gets a date and a note on what to double check.
Reader emails shape the next round. A good number of our tools exist because someone wrote in and asked for them.
What we won't do
We won't ask you to sign up to see a result. We won't store your inputs on a server. We won't dress up an estimate as advice, and we won't bury a disclaimer in tiny type.
We also try not to publish pages just for traffic. A tool should answer a real question, and the article around it should help you understand the answer.
Who it's for
Students working out a grade. Freelancers setting a price. Pet owners curious about age. Developers who need a color converted. People who don't want to open a spreadsheet for a five-minute question. If that sounds like you, you're in the right place.
What we're working on next
The list of tools keeps growing, and so does the number of guides. We add things when we can build them well, test them and write about them in plain words. Quality matters more to us than speed.
We also keep going back to older pages. Rates change, rules change and typos creep in. Updating is less glamorous than launching, though it's what makes a page worth trusting.
If you have an idea, a correction or a complaint, write to us. Real feedback from real users shapes what we build next more than anything else.