The RunTK Guide

How every tool works, how to get the most out of it, and the science it's built on.

Last updated: October 2026

RunTK is a free set of training tools for runners, cyclists and other endurance athletes. Every tool runs entirely in your web browser: there is no account, no sign-up and no tracking, and your data stays on your device. This guide explains what each tool is for, how to use it, and the research behind the numbers it shows.

Getting started

Open any tool from the main menu, or jump between tools with the menu in the top-left corner of every page. Each tool has a ? button with detailed help for that tool.

Connecting Intervals.icu

Several tools can read from or write to Intervals.icu, a training log and analysis platform. To connect, you need two things:

API key: in Intervals.icu, open Settings and find the API key under Developer Settings.
Athlete ID: enter 0 to mean your own account, or the athlete ID shown next to the API key.

Your key is sent only to Intervals.icu, directly from your browser. It is kept on your device only if you tick Remember API key on this device. Intervals.icu is optional: the Pace Converter and Interval Timer never need it, and most other tools can be used with manual input.

Using tools offline

The Pace Converter, Interval Timer, Nutrition Planner and Long Run Planner can be saved for offline use with the switch on their card on the main menu. Once saved, they open without a connection, which is handy at the track, in the gym or on race day. The other tools need the internet because they load maps, forecasts or your training data.

Where your data lives

Settings, plans and routes are saved in your browser's local storage on the device you're using. They don't sync between devices, and clearing your browser's site data for runtk.com deletes them. See the privacy policy for the full details.

Tool guides

How to use each tool, how its calculations work, and the research behind them.

Pace Converter

Pace Converter converts between running pace and speed (min/km, min/mi, km/h and mph) and between pace and finish time for any distance.

How to use the Pace Converter →

Interval Timer

Interval Timer is a workout timer for intervals, circuits, treadmill sessions and gym work. You type the whole workout as a short expression instead of tapping through menus.

How to use the Interval Timer →

Nutrition Planner

Nutrition Planner plans fuelling and hydration for races and long sessions: carbohydrate, sodium and fluid targets, which gels, chews and drink mixes to carry, and how to mix each bottle.

How to use the Nutrition Planner →

GAP Planner (grade-adjusted pace)

GAP Planner plans a route on a map, or imports one from a GPX, TCX or FIT file or from Intervals.icu. It then predicts your pace and time for every split, taking the climbs and descents into account.

How to use the GAP Planner →

Long Run Planner

Long Run Planner suggests how far your next long run can safely be, based on the longest run you've done recently.

How to use the Long Run Planner →

Random Workout Generator

Random Workout Generator makes picking a session fun. Spin a slot machine or roulette wheel over a pool of workouts you choose, or roll a brand-new random fartlek.

How to use the Random Workout Generator →

Multi-Workout Editor

Multi-Workout Editor loads your planned workouts and training plans from Intervals.icu so you can review and edit many at once. Training plans usually build progression across similar sessions: long runs get longer, and intervals gain reps or intensity. This tool lets you line those sessions up and edit them consistently.

How to use the Multi-Workout Editor →

AI Prompt Generator

AI Prompt Generator turns your Intervals.icu training, wellness and event data into a structured coaching prompt. You paste it into the AI assistant you prefer (ChatGPT, Claude, Gemini or another), so you choose the model and see exactly what data it gets.

How to use the AI Prompt Generator →

Workout Weather Planner

Workout Weather Planner finds the best time to start a workout from the forecast for your location, up to 16 days ahead.

How to use the Workout Weather Planner →

Training questions

Pace charts

The pace per kilometre and per mile for every finish time:

Frequently asked questions

Is RunTK free?

Yes. Every tool is free, with no paid tier, ads or upsells. If you'd like to, you can support RunTK from the About page.

Do I need an account?

No. There are no RunTK accounts. Tools that connect to Intervals.icu use your own Intervals.icu API key, which goes only to Intervals.icu.

Is my data private?

Yes. Everything is calculated in your browser, and RunTK has no server that receives your data. The only outside services are the ones a tool needs to do its job (Intervals.icu, map, routing and elevation services for the GAP Planner, and Open-Meteo for weather), plus Cloudflare Web Analytics, which counts page views without cookies. The privacy policy lists every one.

Does RunTK work on my phone?

Yes. Every tool is designed for phones first and also works on tablets and desktops. You can add RunTK to your home screen like an app, and save the Pace Converter, Interval Timer, Nutrition Planner and Long Run Planner for offline use from the main menu.

What is grade-adjusted pace (GAP)?

Grade-adjusted pace is your pace converted to the equivalent effort on flat ground. A 6:00/km climb up a steep hill may be as hard as 4:30/km on the flat. The GAP Planner uses this in reverse: from your flat pace, it predicts your pace on every part of a hilly route. More in What is grade-adjusted pace?

How many carbs per hour should I take during a race?

It depends on the event length, your sport and how well you've trained your gut. Research supports higher intakes, up to around 90 g/h and beyond, for long events when glucose and fructose are combined. The Nutrition Planner's Carb Calculator has presets for running and cycling. More in How many carbs per hour? Practise any new plan in training before race day.

How much should I increase my long run?

In a large 2025 cohort study, runs more than 10% longer than your longest run in the previous 30 days came with a higher overuse-injury rate. The Long Run Planner uses those thresholds. More in How much should you increase your long run?

RunTK's tools are for planning and education. They aren't medical advice, and the right numbers for you depend on your health, experience and goals.