Why I built this
I'm a software engineer, not a banker. I started building these calculators because every time I tried to work out a real financial number online, I hit the same three problems: the tool showed a flattering half-answer, it wanted my email before showing results, or it never explained where the number came from.
So the rules here are simple. Every calculator shows the complete number, including the parts people forget. Every formula is printed on the page so you can verify it. Nothing asks you to sign up, and nothing you type leaves your browser — the math runs on your own device.
The calculations are covered by automated tests that check them against standard finance results, because on a money site "probably right" isn't good enough.
What "the whole number" actually means
Most mortgage calculators answer a question nobody asked. You type in a price and a rate, and out comes principal and interest — a figure you will never actually pay, because it leaves out property tax, homeowner's insurance and mortgage insurance. On a $400,000 house those three can add $600 or more to the monthly cost. A calculator that omits them is not simplifying; it is answering a different question and letting you believe it answered yours.
The same gap shows up everywhere. Auto loan tools that ignore sales tax and registration. Credit card payoff tools that quietly assume you stop using the card. Retirement calculators that project a balance without ever mentioning that the money will be taxed on the way out. Each one produces a number that is arithmetically correct and practically useless.
Every calculator here is built to answer the question you actually have — what will this cost me, or what will I actually have — and to name the assumptions it had to make to get there.
How to get a useful answer out of these
Use your real numbers, not round ones. A rate of 6.85% rather than "about 7" changes a 30-year mortgage by thousands. If you have a quote or a statement in front of you, type what it says.
Run the pessimistic version too. Every one of these tools lets you change the assumptions. Put in a worse rate, a longer term, a lower return. If the decision still works, it is a robust decision. If it only works on the optimistic settings, that is worth knowing before you sign rather than after.
Check the formula. It is printed under every result. If a number looks wrong to you, you can see exactly how it was reached instead of having to trust it — which is the entire reason it is printed.
What these calculators cannot do
They do not know your circumstances. A mortgage calculator cannot tell you whether the neighbourhood is right, whether your job is secure, or whether you would sleep badly carrying that payment. A retirement calculator does not know your health, your family, or what you actually want your later years to look like. These tools handle the arithmetic so you can spend your attention on the parts that are genuinely a judgement call.
They also cannot replace professional advice on anything complicated. Tax treatment in particular varies by state, by filing status and by year, and a general-purpose calculator cannot model that responsibly. Where a decision is large or unusual, the arithmetic here is a starting point for a conversation with a licensed professional, not a substitute for one.
Nothing you type is sent anywhere
Every calculation on this site runs in your own browser. Your salary, your debts, your house price and your retirement balance are never transmitted, never stored and never seen by anyone, including me. There is no account to create and no email field standing between you and the answer. Once a page has loaded it will keep working with the network switched off, which is the simplest possible proof that your figures are staying on your device.