Health tools and calculators
The LifeWell tools directory is a browsable index of small, single-purpose tools: four calculators built into LifeWell, the trackers that save readings to your account, and links out to the stateless calculators on ZTools. Everything here does arithmetic on numbers you type. Nothing diagnoses anything, nothing infers anything about you, and nothing is sent anywhere unless you are signed in and choose to save a reading to your own record.
What people use it for
Working out one number, once
You need a ratio, a percentile or a target and you need it now, on a phone, without an account. The calculators run entirely in the browser, so there is nothing to install and nothing to sign up to — and closing the tab is genuinely the end of it.
Finding the tracker rather than the calculator
A calculator answers a question once; a tracker answers it over months. The directory marks which is which, so a search for "blood pressure" leads to the log that keeps readings rather than a page that forgets them the moment you leave.
Checking what a number does not mean
Every tool page states its source, its assumptions and its limits before it states a conclusion. That is often the more useful half — a threshold crossed by 0.01 means far less than the shape of the same measurement over six months.
Getting to the right site quickly
Most general calculators live on ZTools rather than here, and the cards say so on their face before you click. The split is deliberate: LifeWell keeps the tools that hold your data, ZTools keeps the ones that do not need it.
How it works
- Search or filter — Type what you are after, or pick a category. Both live in the URL, so a filtered view can be shared or bookmarked and survives a refresh.
- Read what the card says it is — Cards are marked when they save data to your account, and when they lead to ZTools rather than staying here.
- Open the tool — Calculators work signed out and offline. Trackers need an account, because they have somewhere to put what you enter.
- Read the method, not only the number — Each tool page names its published reference where it has one, and says plainly where it is approximating.
Questions
Do I need an account to use these?
Not for the calculators. They run in your browser, work with no connection at all, and store nothing. The trackers need an account for the obvious reason that they save what you enter and show it back to you later.
Why do some tools link to another website?
General-purpose calculators live on ZTools, a sister site. LifeWell keeps the tools that hold your data and the handful ZTools does not have. Duplicating a calculator that already exists there would mean two versions to keep correct, which is how one of them quietly goes wrong.
Is any of this medical advice?
No. These tools do arithmetic on numbers you type. They cannot see your history, they do not diagnose, and a result outside a normal range is a reason to talk to a doctor rather than a conclusion in itself.
Where do the reference values come from?
Each tool names its own source on its own page — the WHO Child Growth Standards, the WHO waist-hip thresholds, the Institute of Medicine weight-gain ranges. Where a tool approximates rather than implements a published table, its method section says so explicitly.
Is anything I type sent anywhere?
No. The calculators make no network request to do their arithmetic. What you typed appears in the address bar so a refresh does not lose it, and that is the only place it goes unless you save the reading to your account.
Can I suggest a tool?
Yes, through the contact page. The four calculators kept in LifeWell are here precisely because they were missing elsewhere, so a gap worth filling is worth hearing about.
Tips
- Filter first, then search. A category plus two words finds things faster than one long phrase.
- The URL carries your filters — send it to somebody rather than describing what you searched for.
- A calculator page is worth reading once for its method section, even if you only ever want the number.
- If a tool saves data, use it from the same account as everything else. A reading beside the rest of your record is worth more than one on its own.
By Ahsan Mahmood · updated 2026-07-30
Open Health tools and calculators on LifeWell