The practical stuff, handled.
Finance calculators, privacy tools, statistics utilities, and health checks. Everyday tools that don't need a login or a subscription.
Some calculations deserve a tool.
Not a formula box buried in a blog post.
Search for “COGS formula” on a Tuesday night and Google hands you twenty SEO-bait pages with a dirty calculator buried below the fold. Search again Thursday morning and you type the same numbers again, because nothing saved. There's a quiet tax on that workflow, multiplied by every calculation a normal person quietly Googles two or three times a month.
The usual alternative is a spreadsheet cell with a formula you half-remember. That works the first time. Two weeks pass, you open the sheet, and you're squinting at =(B2-B3)/B2 trying to recall whether you divided gross profit by revenue or the other way around. Google it. Rebuild. Run the number. Close the tab. Forget it by next month. No single instance is expensive. The pattern just compounds quietly, and nobody notices.
The second usual alternative is the first calculator on page one of Google, which is almost always owned by someone who'd like to sell you something related. A mortgage site pretending to be neutral while funneling you to a lender partner. A BAC tool that opens with a liquor store ad. A COGS page optimized for Shopify affiliate commissions. A p-value calculator wedged under a banner for an online graduate program. The math is real. The page around it isn't. That's a weird frame for a number you're going to make a decision with.
What most free calculators online get wrong
- 01
The inputs are personal
Income, body weight, drinks consumed, home price, BAC. These are the inputs advertisers would love to have sitting next to your IP address. Server-side calculators rarely have a reason to collect them. Plenty do anyway.
- 02
The work doesn't persist
Close the tab and the state vanishes. The next session starts from scratch. A spreadsheet fixes the persistence problem at the cost of rebuilding the formula every time you open it.
- 03
The formula is invisible
You get a number. You don't see how. When a professor or a boss asks how you got there, you can't show the steps. A decent tool explains itself with the math it used.
- 04
Edge cases get rounded off
Four distributions for a p-value, not one. Custom ABV per drink, since a 9% IPA isn't the same as a 5% lager. Freight-in as a proper line item, not a footnote. Eighteen real materials in the density table, not one generic formula. Default forms are wrong for most real situations.
- 05
Every result costs three ad impressions
The answer sits at the bottom of a wall of affiliate offers and newsletter prompts. By the time you scroll past it all, you've forgotten what you came for.
- 06
The privacy disclaimer is at the bottom
Any page calculating personal inputs should tell you upfront what happens to them. Most don't. The privacy link gets stuffed into the footer next to the terms of service, far from the form where it would actually matter to read it.
A BAC calculator that phones home is a BAC calculator you shouldn't trust. Same with your down payment, your margin, your test statistic, your sample weight. The math isn't the sensitive part. The inputs are.
Keep it in the browser.
What the tools in here actually do
Perclo shows every down-payment percentage on one screen with real PMI rates by LTV band, so you stop running the same scenario four times. For ecommerce sellers, Cogsly handles COGS alongside gross profit and margin, and puts freight-in and direct expenses on the form where they belong. Massvo goes in any direction across density, mass, and volume. It mixes metric and imperial freely and ships with eighteen materials you can click to prefill.
Pvalr covers Z, T, chi-square, and F distributions with a plain-English read on whether your statistic clears the bar you set. Sober uses the Widmark formula with custom ABV per drink (a 9% IPA and a bar double aren't the same drink), color-coded against the legal limit, with a countdown to when your estimated BAC hits zero. Blank strips GPS coordinates, device serials, and whatever else the camera put in the EXIF header, before the photo goes anywhere. All of it client-side. Nothing phones home.
These are tools we built because we kept reaching for them and couldn't find decent versions online. The catalog keeps growing, and the approach stays the same. Open the page, type your numbers, read the result, close the tab. Nothing saved unless you explicitly save it. Nothing sent unless you sent it. Somewhere out there is the fifth person this week Googling a p-value threshold, or the Widmark coefficient for body mass, or the right way to deduct freight from ending inventory. The right answer is almost never the sponsored link at the top. It's a single tab that remembers what it's for, loads in under a second, and doesn't ask for anything in return. A quiet tool. A fast one. Built right the first time.
Everyday Tools
See what your photos are hiding, then strip it.
Phones bake location, device model, and often the serial number straight into every photo they take. Social platforms sometimes strip that header before posting. Often they don't. Blank reads what's in there before you share. GPS coordinates, device IDs, timestamps, plus whatever else the camera manufacturer decided to embed. Batch processing handles up to twenty images at once, with a one-click wipe on the output and a ZIP download when you're done. Everything runs in the browser, so nothing uploads. JPEG, PNG, WebP, HEIC all supported.
Try it 02Compress images in your browser. No uploads. No limits. No account.
TinyPNG and Optimizilla batch-compress images by uploading them to a server. Squoosh keeps files on-device but only handles one at a time. Komprs runs an unlimited batch entirely in the browser through OffscreenCanvas and a Web Worker, so the files never leave the machine. A global quality slider updates estimated output size across the whole queue in real time, and a split-slider before/after viewer moves with it so you can watch where the artifacts start. JPEG, PNG, and WebP in and out. Download per file, or grab the whole set as a zip.
Try it 03COGS, gross profit, and margin in one calculation.
Every free COGS calculator online gets you halfway. You type your numbers, get cost of goods sold back, and then open a separate tab for gross profit and margin. Cogsly does all three at once. Freight-in and direct expenses are first-class fields instead of a footnote, and the step-by-step formula breakdown shows the arithmetic as it happens. That matters when you're checking the number against what your accountant sent back. Nothing hits a server. Built for Shopify and Etsy sellers who shouldn't need accounting software for a margin check.
Try it 04Every down payment scenario, side by side.
"How much do I need for a down payment?" has at least four right answers. Each one shifts your monthly payment. Some trigger PMI. All of them change what you need in cash at closing. Most calculator sites hand you one scenario per page, so you end up with four tabs open. Perclo puts 3%, 5%, 10%, and 20% side by side with real PMI rates by LTV band and total closing cash on the same line.
Try it 05The compound interest calculator that doesn't get in your way.
Incumbent compound interest calculators make you press a button to see the result, then bury the year-by-year table under a signup funnel. Accruo skips both. Initial balance, monthly contribution, rate, and years are linked sliders and number fields. The stacked chart updates as you drag, splitting principal, contributions, and interest. The full year-by-year table sits right below, no pagination, sticky header. Five contribution frequencies, four compounding frequencies. Validated within a dollar of SEC Investor.gov reference output. Nothing leaves your browser.
Try it 06Test statistic in, p-value out. 30 seconds.
Looking up whether a test statistic of 2.31 clears significance at alpha = 0.05 with 14 degrees of freedom used to mean digging through a table in the back of a textbook, or opening R for a one-line call. Pvalr does it in a form field. Z, T, chi-square, F. One-tailed or two. Custom alpha. Degrees of freedom where they belong. Output is the p-value, a plain-English verdict on whether it clears the bar you set, and a reminder that low p-values don't measure effect size. Client-side through jStat.
Try it 07Am I intoxicated? How long until I'm sober?
Most BAC calculators assume standard drink sizes and strengths, so the number's wrong the moment you're measuring anything real. Sober takes custom ABV per drink. A 9% IPA and a 5% lager aren't the same drink, and a bar double isn't either. The math is the Widmark formula, the one used in forensic toxicology. You get a color-coded result against the legal limit plus a countdown to when your estimated BAC hits zero. Nothing saved, nothing sent.
Try it 08Density, mass, volume — solved and explained.
Density, mass, volume. You know two, you want the third. Massvo solves in any direction, mixes metric and imperial freely (pounds for mass, liters for volume, g/cm³ out if that's what your spec sheet wants), and walks through the formula with your numbers substituted so you can actually show your work. Eighteen materials sit in a reference table. Click any one to prefill the density and solve from there. A buoyancy indicator tells you whether the result would float in water without making you look it up.
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