Math Notepad

A calculator that works like a notepad

Most calculators make you think in one expression at a time, and then they forget it. A math notepad does the opposite: you write a whole problem out as text, one idea per line, and an answer appears next to each line as you type. Change the number on line two and every line below it updates. Nothing is hidden behind a history button, because the history is the document.

It reads the way you would say it. Type $2,400 - 15% and you get the discounted price. Type 180 lbs to kg and you get kilograms. Type total under a list of costs and you get the sum. Everything runs locally in your browser, so the numbers you are working with, whether that is a salary, an invoice, or a client quote, never leave your device.

How to use it

1. Start typing on the left. One calculation per line. Blank lines and lines beginning with # are notes.
2. Read the answer on the right. Results line up with the line that produced them. Click any result to copy it.
3. Name things you reuse. Write rate = 85 USD once, then use rate for the rest of the sheet.
4. Keep going on the next line. Start a line with an operator, like - 15%, and it carries on from the line above.
5. Add up a block. List your numbers, then write total on the next line. A blank line starts a new block.
6. Keep separate problems in separate tabs. Add a sheet with New, rename it by double-clicking the tab. Everything is saved as you type.

What you can write

The parser understands units, currencies, percentages and dates, plus roughly two hundred mathematical functions. These are the patterns worth knowing.

Common use cases

• Quoting freelance work. Set a rate, multiply by hours, add tax, take a deposit percentage, and keep the whole calculation to send on.
• Splitting a bill or a trip budget. List the costs, mix currencies freely, and write total and average underneath.
• Working through a discount or a markup. Compare 20% off against a flat reduction without resetting anything.
• Converting recipes and measurements. Ounces to grams, cups to millilitres, Fahrenheit to Celsius, in one sheet.
• Sizing engineering numbers. Bandwidth, storage, request rates and durations, with the units carried through the arithmetic.
• Planning around dates. Deadlines, notice periods, and how many days are left until a launch.

Private by construction

There is no account, no upload and no server-side evaluation. The math engine is a JavaScript library loaded into the page, your sheets sit in your browser's local storage, and the only request that leaves the page is a single fetch for exchange rates that carries none of your text. If you are pricing a contract or working through personal finances, that difference matters more than any feature.

Frequently asked questions

Is anything I type sent to a server?

No. Every calculation is parsed and evaluated by JavaScript running in your browser, and your sheets are stored in your browser's local storage on this device. Nothing is uploaded, nothing is logged, and there is no account. The only network request the page makes is a single call for currency exchange rates, which sends no part of your text.

Are my sheets still here when I come back?

Yes. Every tab and everything you typed in it is saved locally as you type, so closing the tab or restarting your browser picks up exactly where you left off. Because storage is per browser and per device, sheets do not sync between your phone and your laptop, and clearing site data removes them.

How many sheets can I keep open?

Up to twelve at once. Use the New button to add one, double-click a tab (or use the pencil button) to rename it, and the close button to remove the one you are on. Closing the very last sheet empties it instead of leaving you with no editor.

What can it actually calculate?

Arithmetic with proper operator precedence, percentages in every phrasing, unit conversion across length, mass, volume, area, temperature, time, speed, data and more, live currency conversion for over 500 currencies and crypto assets, named variables, references to earlier lines, running totals and averages, and simple date arithmetic. It also keeps the full mathjs function library, so sqrt, log, sin, round, gcd and roughly two hundred others work.

Can I keep working on the previous line?

Yes. Start a line with an operator and it carries on from the line above, so you can write 2,400 USD on one line, then - 15% on the next, then + 90 USD after that, and watch the running figure change. The space after the operator is what tells it apart from a negative number: - 15 continues the line above, while -15 is minus fifteen. A continuation takes the place of the line it revises when a total is worked out, so nothing gets counted twice.

How do totals work?

The word total (or sum) adds the results of the lines directly above it, stopping at the first blank line or comment. That is what makes a sheet feel like a list rather than one long expression: type a heading, list your costs, then write total. The word average works the same way, and prev refers to the single line above.

Where do the exchange rates come from?

The Coinbase public exchange-rate API, fetched once when the page loads. Rates are indicative and meant for everyday estimates, not for settling trades or filing accounts. If the request fails, everything except currency lines keeps working.

How is this different from a normal calculator?

A normal calculator forgets. Here the whole calculation stays visible as editable text, so you can go back and change the tax rate on line 2 and watch every line below it update. You can leave yourself notes with #, name your values, and keep separate sheets for separate problems.

Is this like Numi or Soulver?

It solves the same problem: a scratchpad where plain-language lines produce answers. This one runs in any browser rather than as a native app, costs nothing, and keeps your sheets on your own device. It is an independent implementation and is not affiliated with either product.

Why did my line show an error?

Usually one word was not recognised. Currency codes need to be real codes or symbols, unit names must be ones the engine knows (write minutes rather than m, for example), and a variable has to be defined on an earlier line before you use it. Errors are contained to that one line, so the rest of the sheet keeps computing.

Does it work offline?

The calculator does, once the page has loaded. Currency conversion needs the one rate request, so those lines will not resolve without a connection, but arithmetic, units, percentages and dates all keep working.