Notes

FitCalc: Calculators Written Like a Coach's Notebook

Published 2026-09-14 · 7 min read

FitCalc is a small set of training and nutrition calculators — TDEE, protein intake, a fat-loss timeline, one-rep max, and intermittent fasting — plus guides that go with each one. It exists because I almost bought a finished calculator site instead of building one, and looking closely at what I was about to buy talked me out of it.

The site I almost bought

There's a small industry of single-purpose calculator sites sitting on exact-match domains — the URL is literally the search term. I found one for sale, priced at a multiple of its monthly profit that looked reasonable on paper, and came very close to buying it. Then I looked at its traffic: a little over 1,700 visits a month, on a domain that matches the search term exactly. If owning the perfect domain name for a query only pulls in that much traffic, the query itself is small — the domain wasn't holding the site back, the ceiling was just low. What would matter more than the name was who stands behind the numbers, and that is something a purchase can't bring with it.

The one thing a competitor can't copy

Any calculator can be rebuilt in an afternoon; the formulas involved are published and not secret. The thing an anonymous site can't manufacture is a real person willing to put their name and actual certifications behind the numbers. FitCalc is written and reviewed by a certified personal trainer — ISSA and PESA certified, across ten certificates covering personal training, nutrition coaching, corrective exercise, and strength and conditioning, all of them shown on the site rather than just claimed. That's the asset a copy-paste competitor doesn't have, and every decision on the site is built to protect it: no invented statistics, no borrowed research that hasn't actually been read, and every equation used is either a published formula or a range that's widely accepted in the field rather than a number made up to look precise.

Zero-dependency, on purpose

The site is generated by a small Node build script with no framework and no runtime dependency at all — the script reads a set of content files and writes out plain HTML. That sounds like a strange constraint to choose in 2026, but the reasoning is simple: this is a site whose entire value depends on search engines being able to read it, and static HTML never has a rendering problem to debug. There's no hydration step, no JavaScript framework deciding what a crawler sees first, no build pipeline that can quietly regress. A calculator page ships as a finished document; the JavaScript on it only runs the arithmetic once you fill in the form, not the page itself.

Writing a result like a coach would say it

The part of the design I care most about isn't the layout — it's what happens after you hit calculate. Most calculator sites hand you a table of numbers and stop. FitCalc's results lead with one number, large, and a sentence underneath that reads like something a coach would actually tell you, not a spreadsheet output: your maintenance calories are an estimate, not a measurement, and the number that actually matters is what your weight does over the next two weeks of eating at that level. That framing isn't decoration — it's the difference between a tool that hands you a figure and one that tells you what to do with it. Every calculator on the site follows the same shape: the number, then the sentence that turns it into a decision.

The cache bug that shipped old designs to returning visitors

One lesson worth writing down: early on, the stylesheet had a fixed filename and a long browser-cache lifetime, which is normally a reasonable combination for a static site. It went wrong the first time the design changed — anyone who had opened the site before kept seeing the old stylesheet for as long as their browser's cache considered it valid, because nothing about the request told the browser the file underneath had changed. The fix was to put a content hash in the filename itself, so a new design produces a new filename automatically and an unrelated visit to an unchanged page keeps using the cached copy. It's a one-line change in the build script, but it's the kind of bug that's invisible in your own browser, because you're the one person guaranteed to have cleared the cache recently.

The calculators and guides

Five calculators are live: a TDEE and calorie target calculator, a protein intake calculator, a fat-loss timeline calculator, a one-rep max calculator, and an intermittent fasting calculator. Each one sits next to guides that explain the reasoning behind it in more depth than a results page has room for — among them how TDEE is actually estimated, how much protein you actually need, and how to estimate a one-rep max without testing it directly.