Everyday Money Calculators: Which One Do You Need?
This category covers two very different kinds of questions — quick arithmetic you need in the moment, and bigger financial decisions worth modeling properly. Here's both groups.
Quick arithmetic (answer in seconds)
- Any percentage problem — Percentage Calculator: X% of Y, what percent X is of Y, or percent change, all on one page.
- Splitting a restaurant bill — Tip Calculator: tip, total, and per-person split with sensible presets.
- Working out a sale price — Discount Calculator, including stacked discounts and sales tax.
- Converting between currencies — Currency Converter, using live daily exchange rates.
- Figuring out embedded or added tax — VAT / Sales Tax Calculator, in either direction.
Bigger decisions (worth modeling properly)
- Renting vs. buying a home — Rent vs. Buy Calculator compares the true cost of both, including what a down payment could otherwise earn invested.
- How much car you can actually afford — Car Affordability Calculator, using the conservative 20/4/10 budgeting rule.
- Building a safety net — Emergency Fund Calculator, sized from your real monthly expenses.
- Where you actually stand financially — Net Worth Calculator — everything you own minus everything you owe, in one number.
All everyday tools
- Percentage Calculator Three percentage problems, one page: X% of Y, what percent X is of Y, and percent change.
- Tip Calculator Tip, total, and per-person split in one glance — with sensible presets for quick math.
- Discount Calculator Final price after a discount — including stacked second discounts and sales tax.
- Rent vs. Buy Calculator Compare the true cost of renting against buying over time, including the money buying ties up.
- Net Worth Calculator Add up what you own and subtract what you owe to see your real net worth in one number.
- Car Affordability Calculator Find the car price that fits your budget using the 20/4/10 rule on your income.
- Emergency Fund Calculator Find your target emergency fund from your monthly expenses, and how long it takes to build.
- Currency Converter Convert between world currencies using live daily exchange rates.
- VAT / Sales Tax Calculator Add tax to a price, or pull it back out of a tax-inclusive price, with presets for common VAT and sales tax rates.
Frequently asked questions
What's the difference between the Discount Calculator and the VAT Calculator?
The Discount Calculator answers "what do I pay after a markdown" — including stacked discounts, like 20% off then an extra 10% off. The VAT Calculator answers a different question: how much tax is embedded in (or should be added to) a price. They're often used together — figure the discounted price first, then check the tax on that final number, not the original sticker price.
Is the Rent vs. Buy Calculator biased toward one answer?
No — it's built to give an honest number either way, and which one wins depends entirely on the inputs: local rent, home price, how long you'll stay, and what the money tied up in a down payment could otherwise earn invested. Feed it your real numbers rather than assuming the answer; the calculator exists because the popular "renting is throwing money away" and "buying is always better long-term" lines are both oversimplified.
How is the 20/4/10 rule in the Car Affordability Calculator different from what a dealer or loan officer tells me I can afford?
Dealers and lenders often qualify you for the maximum loan your income and credit can support — not the maximum that's actually comfortable. The 20/4/10 rule (20% down, 4-year loan or shorter, total transportation costs under 10% of gross income) is a conservative, widely-cited personal-finance guideline aimed at leaving room in your budget, which is usually a stricter number than what you'd get pre-approved for.
How big should my emergency fund actually be?
The Emergency Fund Calculator works from your real monthly expenses, not an arbitrary flat number — the common guidance of "3 to 6 months of expenses" only makes sense once you know what a month of your expenses actually costs, which varies enormously person to person. Enter your real numbers and it shows both the target and how long reaching it takes at your current savings rate.