Editorial Policy

Christian Lassen Dam writes, builds and maintains everything here. I am 25, I live in Aalborg in Denmark, and I am an MSc student in Mechanical Engineering at Aalborg University. I have been riding Zwift for years, I own the Tron bike, and I am currently training for Ironman Copenhagen. That combination is the whole qualification: an engineer's habit of fitting curves to data, plus enough hours on the trainer to know when a model is giving an answer no real rider would recognise.

There is no editorial team, no fact-checking department and no panel of outside reviewers. It is one person. Saying so is more useful to you than inventing a masthead, because it tells you exactly whose judgement you are trusting and where to send a complaint. You can read more about my background on the author page and about why the site exists on about us.

The site is operated by my company, CLD Consulting, CVR 45654230, Krøyer Kielbergsvej 10, 8660 Skanderborg, Denmark. That is the legal entity behind the domain, the advertising account and any contract the site enters into.

Every factual claim on the site sits somewhere in a four-level hierarchy, and I try to work as high up that list as the question allows.

1. Primary sources and peer-reviewed work. Physiology, aerodynamics and training-load claims are taken from published research or from textbooks that summarise it. If a study is the basis for a statement, the study is what gets described, not a second-hand blog summary of it.
2. Zwift's own published material. Route distances, elevation profiles, game mechanics, unlock rules and pricing come from Zwift where Zwift has published them.
3. Well-established community measurement. Zwift does not publish everything, and for the gaps the community has done careful work over many years. Route data and equipment testing from sites such as ZwiftInsider fall here. This is good data, but it is measured by riders rather than by the developer, so it is labelled as community measurement.
4. Reasoned estimation. Sometimes there is no measurement and the honest thing is to reason from physics and say so. Estimates are always marked as estimates, in the sentence that contains them, not in a disclaimer at the bottom of the page.

Two rules follow from that hierarchy. In an article, any number presented as measured carries a link to the place it was measured, so you can check it yourself. Any number that came out of a model is described as modelled, with the model stated. If I cannot do either, the claim is either rewritten as reasoning or removed. The same rule applies to comparisons like Alpe du Zwift against Ven-Top, where the route facts are sourced and the time predictions are explicitly model output.

The pipeline behind a climb calculator is not complicated, and it is worth stating plainly.

First, gather finishing times paired with the rider's power-to-weight ratio for that effort. Second, fit a curve through the pairs. Third, check the fit against landmarks I can reason about independently, such as what a rider at a known W/kg has to hold to go under an hour. Fourth, publish the equation itself rather than hiding it behind a button. Fifth, revise it when reader-reported results consistently disagree with what it predicts.

For Alpe du Zwift, which is 12.2 km with 1,036 m of gain across 21 hairpins at roughly 8.5% average gradient, the fitted relationship used by the Alpe du Zwift calculator is:

time_seconds = 148.60 * (W/kg)^2 - 1954.08 * (W/kg) + 8329.87

The method behind that fit, including why a quadratic is a reasonable shape for this relationship and where it starts to misbehave, is written up in the regression analysis methodology article. The same approach produces the estimate on the Ven-Top calculator, for a climb of roughly 20.9 km and somewhere between 1,480 and 1,534 m of gain. That spread is a good example of the hierarchy in practice: the figure depends on where the measurement starts, so the Ven-Top guide gives the range with its sources rather than picking one number and sounding certain.

The limits are real and I would rather you hear them from me. The estimate assumes steady power for the whole climb. It assumes no in-game draft on the climb, which is usually true on the Alpe but not always. And it assumes a rider who does not blow up, which is the assumption most often broken in practice. Go out 0.3 W/kg above what you can hold and the model will be optimistic, sometimes by minutes. Treat the output as a target to pace against, not as a promise. The other tools carry the same caveat, including the FTP calculator and the racing category calculator.

Large language models are used on this site, and pretending otherwise would be the opposite of an editorial policy. Here is the actual division of labour.

A model helps with drafting and structuring: turning notes into paragraphs, proposing an outline, tightening sentences that ran long. That is where it stops. A human decides what the article argues. A human checks every number against its source. A human clicks every link before it ships. Nothing on this site is published unread, and nothing is published that I would not defend in a comment thread.

What a model is never allowed to do is supply a fact. It does not get to produce a statistic, a study citation, a URL, or a quote that then goes on the page. Those are the exact failure modes that make AI-assisted writing untrustworthy, and every one of them is caught at the human step or the sentence does not survive.

Google's own guidance judges content by whether it is helpful, original and reliable rather than by how it was produced. I think that is the right test, and it is the one I hold the site to. If a page would not be worth reading had it been typed by hand, the tool used to draft it does not save it.

If something here is wrong, tell me. Use the contact page or email zwiftcalculator@gmail.com. The most useful report names the page, quotes the sentence, and says what the right answer is and how you know. Calculator disagreements are especially welcome: your finishing time, your weight, and the average power you held tells me more than any amount of theorising.

What happens next is straightforward. I acknowledge the report. I check the claim against its source. If it is wrong, the page is fixed. If it is right but badly phrased, the phrasing is fixed. If I disagree, I say why rather than quietly leaving it.

A corrected page says that it was corrected. Substantive fixes, meaning anything that changes a number, a conclusion or a recommendation, get a dated correction note on the page itself. Typos and broken links are repaired silently, because nobody needs a changelog for a missing comma. What will not happen is a wrong figure being swapped for a right one with no trace that the wrong one was ever there.

Everything on this site is free to use, and display advertising is what pays for the domain, the hosting and the time. That is the entire business model.

Advertisers have no say in what gets written. They do not see articles before publication, they cannot request coverage, and they cannot request that coverage be removed. There are no sponsored articles. There are no affiliate links, so no recommendation on this site earns me a commission if you act on it, and no product is praised because it happens to pay better.

If any of that ever changes, the disclosure will appear on the page it applies to, at the top, in plain language, not buried in a site-wide footnote. The commercial terms of using the site are set out in the terms of service.

The calculators run entirely in your browser. Your weight, your power numbers and your finishing times are used to render a result on your screen and are never sent to a server, never stored, and never associated with you. There is no account to create and nothing to log in to.

The site does use analytics and third-party advertising, which involve cookies and similar technologies. What is collected, why, and how to exercise your rights under GDPR or CCPA is set out in full in the privacy policy.

It is not medical advice. Nothing here is written by a doctor or a physiotherapist, and nothing here accounts for your health history. If you have a heart condition, are coming back from injury or illness, or are new to hard exercise, talk to a medical professional before you follow any training suggestion you read on this site.

It is not coaching. A coach watches your data over months, knows your calendar, and adjusts when life gets in the way. A calculator gives you a number. The articles in the training category explain principles, but they cannot see your last four weeks and they are no substitute for a real coaching relationship.

It is not affiliated with Zwift Inc. This is an independent fan-built site. Zwift does not review, endorse, sponsor or check anything published here, and all Zwift trademarks belong to Zwift Inc.

Zwift changes. Routes get adjusted, physics get tuned, categories get redefined, and a page that was accurate in March can be quietly wrong by September. So the site is re-checked on a schedule rather than only when someone complains.

Calculator pages and the reference data behind them, meaning route distances, elevation figures and gradient averages, are reviewed at least twice a year, and again whenever Zwift ships an update that touches route geometry, drafting or climbing physics. The climb reference pages and the FAQ are checked in the same pass. Fitted equations are re-examined when reader-reported times start to cluster on one side of the prediction.

Articles carry publication dates on the blog index, so you can see how old a piece is before you rely on it. An old article is not automatically wrong, but with a game that ships updates this often, the date is information you should have.