TL;DR: LaChart is a surprisingly capable free lactate analysis tool built by a single developer, Jakub Stadnik. It offers lactate curve generation, multiple threshold detection methods (OBLA, IAT, Dmax, Log-log, LTP1/LTP2), training zone calculation, historical test comparison, and even Strava integration. For a donation-funded project, the feature set is impressive. But “free” comes with tradeoffs: no coaching workflow, no communication tools, no workout builder, limited development resources, and real questions about long-term sustainability. If you need a quick lactate calculator, LaChart is hard to beat. If you need a tool that fits into your daily coaching, you’ll hit its ceiling quickly.
What Is LaChart?
LaChart (lachart.net) is a web-based lactate curve calculator and testing app. It runs entirely in the browser as a React single-page application, works on all devices, and requires no installation. The tool was built by Jakub Stadnik, and it’s funded through donations (Buy Me a Coffee) and Google AdSense rather than through paid subscriptions or licenses.
At its core, LaChart does one thing well: it takes your lactate test data and turns it into a curve with threshold markers and training zones. You can use it without even creating an account, which makes it one of the most accessible lactate analysis tools available. Just open the site, enter your data, and get a curve.
For coaches who create an account, LaChart adds athlete management, historical test comparison, a training calendar with TSS analytics, and Strava integration. There’s also a coach role that lets you manage multiple athletes, which is more than you’d expect from a free tool.
Key Features
Lactate Curve Generation
The core of LaChart is its curve calculator. Enter your step test data (power or pace, heart rate, lactate values at each stage), and LaChart generates a lactate curve with threshold markers. The interface is clean and modern, with a React-based UI that feels contemporary and responsive.
You can use the calculator without registration, which is a nice touch for coaches who just want to quickly visualize a test result. No signup walls, no email collection, just the tool.
Threshold Detection Methods
This is where LaChart genuinely surprises. For a free tool, the range of threshold methods is solid:
- OBLA (Onset of Blood Lactate Accumulation): Configurable from 2.0 to 3.5 mmol/L
- IAT (Individual Anaerobic Threshold)
- Dmax method
- Log-log method
- LTP1/LTP2 (Lactate Turning Points)
- Baseline + Delta method
Most coaches will find the methods they actually use in practice. You won’t find every obscure variant that WinLactat offers, but the coverage is genuinely practical.
Training Zone Calculation
LaChart calculates five training zones based on your threshold results. The zones are generated automatically, giving you immediate actionable output from a test. For coaches who work with a five-zone model, this is straightforward and useful.
The zone system is less flexible than what you’d find in a full coaching platform where you might want six or seven zones, custom zone labels, or different zone models for different athletes. But for a quick, standard zone calculation, it does the job.
Historical Test Comparison
When you create an account, LaChart stores your test history and lets you overlay previous results for comparison. This is genuinely valuable for tracking athlete progression over time. Seeing how the lactate curve shifts across a training season tells a story that a single test can’t.
Strava Integration
LaChart connects to Strava and can pull in activity data. The recent bulk interval detection feature (added November 2025) lets you analyze Strava activities for interval segments, which adds a layer of training analysis beyond pure lactate testing.
Coach & Athlete Management
There’s a coach role that lets you manage multiple athletes within LaChart. You can store athlete profiles, access their test histories, and track their data over time. It’s basic compared to a full coaching platform, but the fact that it exists at all in a free tool is notable.
Training Calendar & TSS Analytics
LaChart includes a training calendar view with TSS (Training Stress Score) tracking. Combined with the Strava integration, this gives coaches a basic picture of training load over time. It’s not a full periodization or planning tool, but it adds context to your lactate data.
PDF Report Generation
Added in March 2026, LaChart now generates PDF reports from test results. This is a welcome addition for coaches who need to share results with athletes in a professional format. The reports cover the essentials: curve visualization, threshold values, and zone recommendations.
FIT File Upload
You can upload FIT files directly to LaChart, which means data from cycling computers and other devices can flow into the platform without manual transcription.
Strengths
It’s Free
Let’s start with the obvious. LaChart costs nothing to use. In a space where most serious tools charge hundreds of euros per year (or more), a free option with this feature set is remarkable. For coaches just getting started with lactate testing, or for individual athletes who want to track their own data, the price barrier simply doesn’t exist.
Modern, Clean Interface
LaChart looks and feels like a modern web application. The React-based UI is responsive, clean, and intuitive. Compared to desktop tools like WinLactat with their traditional menu-driven interfaces, LaChart feels contemporary. It works well on phones and tablets, not just desktops.
No Installation, No Platform Lock
Being entirely web-based means LaChart works on any device with a browser. Mac, Windows, Linux, phone, tablet. There’s no software to install, no Windows dependency, and no updates to manage. You just open the URL and start working.
Surprisingly Deep for a Free Tool
The combination of multiple threshold methods, historical comparison, Strava integration, coach management, and PDF reports is genuinely impressive for a donation-funded project. LaChart isn’t a toy. It’s a functional lactate analysis tool that covers the practical needs of many coaches.
Good Threshold Method Coverage
Supporting OBLA, IAT, Dmax, Log-log, LTP1/LTP2, and Baseline+Delta covers the methods that most coaches actually use. You’re not limited to a single fixed threshold like simpler calculators offer.
Active Development
Recent updates (PDF reports in March 2026, bulk Strava interval detection in November 2025) show that the project is actively maintained and growing. New features are being added regularly, which is encouraging for a one-person project.
Weaknesses
One-Person Project
This is both LaChart’s charm and its biggest risk. Everything depends on a single developer. If Jakub Stadnik loses interest, gets busy with other work, or simply can’t maintain the project, LaChart could stagnate or disappear. There’s no company behind it, no team, no institutional backing.
For coaches building their practice around a tool, this is a legitimate concern. You’re trusting your workflow and your data to the continued motivation and availability of one person.
Donation-Funded Sustainability
LaChart is funded through Buy Me a Coffee donations and Google AdSense revenue. This model works when a project is small, but it raises real questions about sustainability as the tool grows. Server costs increase with users. Feature requests pile up. Security patches need attention. Bug fixes can’t wait.
Donation-funded open source projects have a mixed track record. Some thrive for years. Others burn out their maintainers. There’s no way to predict which path LaChart will follow, and coaches should factor this uncertainty into their tool selection.
No Coaching Workflow Integration
LaChart calculates zones, but those zones live inside LaChart. There’s no connection to your training planning tool, no workout builder, no way to prescribe training based on test results. After you run a test and see the results, you still need to manually transfer zones into whatever platform you use for daily coaching.
For coaches who run occasional tests, this is fine. For coaches who test regularly and manage many athletes, the disconnect between testing and coaching becomes a real time sink.
No In-App Communication
There’s no way to communicate with athletes through LaChart. You can’t share notes, discuss results, or provide coaching feedback within the platform. Test results exist in isolation from the coach-athlete conversation.
No Workout Builder or Annual Planning
LaChart tracks training (via Strava), but it doesn’t help you plan training. There’s no workout builder, no periodization tools, no annual planning features. The training calendar shows what happened, not what should happen next.
No Spiroergometry Support
For coaches who combine lactate testing with gas exchange analysis, LaChart doesn’t support spiroergometry data. There’s no way to overlay VO2, VCO2, or ventilatory data with your lactate curve.
No Metabolic Profiling Beyond Lactate
LaChart focuses exclusively on the lactate curve. It doesn’t calculate vLaMax, fat oxidation rates, or other metabolic parameters that tools like INSCYD or WinLactat provide. If you want to go deeper than threshold identification, you’ll need a different tool.
Limited Branding and Customization
The PDF reports are functional, but they don’t offer the custom branding options (your logo, your colors, your practice name) that professional coaches often want for client-facing documents.
Multi-Sport Depth
LaChart supports cycling, running, and swimming, which covers the major endurance sports. But the training analytics (TSS-based) are most relevant to cycling. Runners and swimmers may find the analytics less tailored to their needs.
Who Is LaChart Best For?
LaChart is the right choice if you:
- Want a free lactate calculator with no financial commitment
- Run occasional lactate tests and need a quick way to visualize and analyze results
- Are new to lactate testing and want to learn without investing in expensive software first
- Use Strava and want your training data connected to your lactate analysis
- Work with a small number of athletes and don’t need extensive coaching workflows
- Want a modern, web-based tool that works on any device
- Need basic threshold detection with practical zone outputs
Ideal LaChart user: A coach or sport science student who runs periodic lactate tests, wants solid threshold analysis without paying anything, and handles training planning and athlete communication through other tools.
Who Should Look Elsewhere?
LaChart may not be the best fit if you:
- Run a professional coaching business and need your tools to be reliable long-term
- Manage 10+ athletes with regular testing and need integrated workflows
- Want branded, professional reports with your practice identity
- Combine lactate testing with spiroergometry or advanced metabolic analysis
- Need coaching tools like workout builders, annual planning, and in-app communication
- Require institutional-grade reliability with SLAs, support contracts, and a company behind the product
- Want your zones flowing directly into training plans and athlete profiles
Coachbox as an Alternative
If you’ve been using LaChart and are hitting its limits, Coachbox offers a natural upgrade path. The transition addresses the specific gaps that growing coaches encounter with LaChart.
Coachbox’s lactate testing module uses AI-powered analysis to deliver results in under 60 seconds, similar to LaChart’s speed but with automatic LT1/LT2 detection and customizable zone models. The key difference is what happens after the analysis: zones automatically flow into athlete profiles, training plans, and the calendar. There’s no manual transfer step.
You also get professional PDF reports with your own branding, spiroergometry support, in-app communication with athletes, workout builders, annual planning tools, and a full coaching platform that connects everything.
The tradeoff is obvious: Coachbox costs money. LaChart is free. But for coaches whose time has value, the hours saved on manual data transfer, the professional impression of branded reports, and the reliability of a funded platform with 25,000+ users often justify the investment.
Coachbox is hardware-agnostic, just like LaChart. You enter lactate values from whatever meter you own. If you’re already comfortable with the manual data entry workflow, the transition is seamless.
The Bottom Line
LaChart deserves genuine respect. Building a free lactate analysis tool with this feature set, as a solo developer, funded by donations, is an impressive achievement. For coaches who need a quick, capable lactate calculator without spending a euro, it’s the best free option available.
But free tools carry inherent risks. Development depends on one person’s time and motivation. The feature set, while good, stops at the boundaries of lactate analysis. There’s no coaching workflow, no communication, no planning tools. As your coaching practice grows, you’ll likely find yourself copying zones from LaChart into another platform, emailing reports manually, and wishing the pieces were connected.
LaChart is an excellent starting point. For many coaches, it’s also a tool they’ll eventually outgrow. The question isn’t whether LaChart is good for what it does. It is. The question is whether what it does is enough for how you work.