
Critical Swim Speed
CSS Calculator & AI Coach
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$0.99
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About
Know your Critical Swim Speed. Train with purpose. See yourself getting faster.
Critical Swim Speed (CSS) gives you a practical threshold pace for swim training. Complete the standard 400m and 200m CSS test, enter your times, and the app calculates your CSS pace for you.
But calculating the number is only the start.
USE YOUR CSS
• Calculate your Critical Swim Speed from the standard CSS test
• Get a clear pace to use in your swim training
• Find out how to perform the CSS test correctly
TRACK YOUR PROGRESS
• Save every CSS test result
• Visualise your CSS over time and see how your training is progressing
• Add notes about each test so you have context behind the numbers
• Set a reminder for when it's time to test again
ASK THE AI COACH
Get instant answers to questions about your CSS results, swim training and how to improve. The AI Coach is based on my knowledge and experience as a qualified swim instructor, so you can get useful guidance whenever you need it.
Whether you're a swimmer, triathlete or simply someone who likes training with data, Critical Swim Speed gives you an objective benchmark you can test, train with and improve.
Test. Train. Track. Get faster.
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What's New in Critical Swim Speed
2.0.0
September 10, 2026
Critical Swim Speed has had a major upgrade. • A completely redesigned interface that's faster, clearer and more enjoyable to use • New AI Coach — instant Q&A about your CSS, swim training and how to improve, powered exclusively by my coaching knowledge and experience. • New progress visualisations make it easier to see how your swimming is improving over time • Improvements throughout the app to make testing, tracking and reviewing your CSS simpler Same simple CSS test. A much better way to use the result.
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