Adaptive workout app for iPhone and Android
Your workout, written for you in seconds.
Built around your goal, your gear and your time, and checked against a trainer’s standard.
New here? Start with The Opener, a free first week.
Your time. Your workouts. Zero planning.
- It already knows what’s at your gym.
- It already knows you only have 20 minutes.
- It already knows you skipped Tuesday.
- It already knows you hated lunges last time.
So you don’t have to.
No subscription, no card, and the timer is free for good.
How it works
What one tap actually does.
Tell it once
A place, a time, a focus.
That’s all it asks. The rest it remembers.
Hotel room? Hotel workout. Save your spots, switch in one tap, and the workout reshapes itself around whatever’s there.
Watch it build
Written for you, not picked from a list.
It reads your history, weighs your options, and writes a real session: warm-up, working blocks, rest that fits. Most sessions are ready in about five seconds. Not quite right? Rebuild it, or swap a single exercise.
And 35 minutes means 35 minutes. The slider is a promise, not a mood.
Just lift
Press start. Stop deciding.
A calm timer walks you through every set and every rest. What’s next is always on screen. No tapping mid-set, no spreadsheet on the bench.
It even remembers what you lifted last time, down to the kilo.
Checked before you see it
Built to a personal trainer’s standard.
Every session is checked before it reaches you, and most are ready in about five seconds.
Challenges
An app can’t make you show up.
Your group chat can.
A challenge is a workout pact with your crew: same plan, same days, everyone on one board.
- One code joins everyone. Grab a preset or set a goal, then drop the code in the chat. That’s the whole onboarding: no spreadsheet, no group admin.
- Done is a filled cell. Do the day’s workout or hit your numbers and your cell on the board fills in, and your streak grows. Wildcards cover the odd missed day.
- Cheer. Or poke. Fist bumps and fire for whoever showed up. A well-aimed poke for whoever’s slacking. The crew sees who trained, every day.
Not a 75-day bootcamp: rest days count toward the streak, and missing a Tuesday doesn’t burn the whole thing down.
Workout challenges
Kronos builds a fresh workout for the whole crew, on the days you pick. Grab a preset like Daily core, or set the focus, days and length yourself.
Goal challenges
Pick up to 5 movements and the numbers to hit, like 100 squats every weekday. The target climbs each week and the board keeps count.
Under the hood
The machinery behind one tap.
12
workout formats, each with a timer that runs it properly
580
exercises, matched to the equipment actually in the room
16
programs, two to eight weeks, every session still written on the day
5-90min
session lengths, and it finishes when it said it would
44
named workouts in the Library, Cindy to Murph, scored and scaled
0bars
of signal needed. The whole session runs and logs offline.
For the days that don’t go to plan.
21:47. The hotel gym nobody else uses.
The honest part
Five principles. Cited.
The training science Kronos runs on predates every fitness app. It is published, peer-reviewed, and linked at the bottom of this page so you can check our homework.
Time is the unit1,2
Twenty-five minutes is a program, not an apology. Short, hard sessions build real fitness, and the research on that is old news.
Each block has one job3
Strength work does strength. Conditioning does conditioning. Blend them in one block and you blunt both, so each gets its own.
Push while you pull4
Pairing opposing movements saves serious session time at no cost to results. Of every shortcut in the time-efficiency literature, it is the best evidenced.
Scale, don’t substitute5,6
Bad day? The weight drops, the movement stays. You never have to grind to failure for a session to count.
Patterns stay, exercises rotate7,8
You keep squatting; the exact squat changes. Stable patterns build strength, and rotation keeps you from dreading Tuesday.
The receipts
- Gillen et al. 2016, PLOS ONE: three 10-minute sprint-interval sessions a week matched 50-minute steady rides over 12 weeks.
- Iversen et al. 2021, Sports Medicine: "No Time to Lift?" Time-efficient strength programming.
- Schumann et al. 2022, Sports Medicine: concurrent-training interference is small when the signals stay separated; explosive power is the exception.
- Zhang et al. 2025, Sports Medicine: supersets cut session time with similar long-term strength and hypertrophy.
- Refalo et al. 2023, Sports Medicine: training to failure is not required for hypertrophy.
- Zourdos et al. 2016, Journal of Strength & Conditioning Research: the reps-in-reserve scale, most accurate close to failure.
- Fonseca et al. 2014, JSCR: varied exercises within a pattern build more complete development.
- Kassiano et al. 2022, JSCR: systematic, not random, variation for strength and hypertrophy.
What Kronos is not
Not throwing shade. Just being clear about who we’re for.
If you want…
A full lifting logbook
Try…: Strong or Hevy
We log your main lifts when you want it. Living in the spreadsheet is their whole job, not ours.
If you want…
A plan carved in stone
Try…: A PDF program
Kronos programs rewrite themselves around your week. If you want week 7 fixed in advance, that’s not us.
If you want…
A human coach over text
Try…: A coaching service
Real coaches are great. They cost real money.
If you want…
A YouTube workout to follow
Try…: A follow-along channel
Great, but it doesn’t know your equipment, time, or level.
If you want…
An AI chatbot for fitness
Try…: ChatGPT
We already asked it. Here’s today’s workout.
Kronos is for people who tried those things, fell off, and want a workout to show up for, not another system to maintain.
Most fitness apps make you a workout plan. Kronos makes you a person who works out.
The interval timer is free. Forever.
Every mode, with nothing metered and nothing watching. Your whole training history exports as CSV whenever you ask. Your first week of workouts is free too, and one a month after it; Pro is for when you want the deciding done every day. The timer just stays free.
Fair questions.
Is Kronos free?
The interval timer is free forever, no ads, no account. Logging, training offline and joining a challenge are free too, on a free account. That account also comes with a free first week, three workouts across seven days, and one workout a month after it. Kronos Pro takes the caps off, monthly or annual. Your local price is on the pricing page.
What equipment do I need?
Whatever you have. A full gym, a pair of dumbbells, a hotel room floor. Tell it once and every workout is written from what’s actually there.
How is this different from a workout program?
Kronos has programs, but none of them are fixed. A program here holds the arc (build weeks, a deload, a test at the end) while every session inside it is still written for the day you’re actually having: your time, your equipment, your recent training. There’s no week 7 to fall off of, because week 7 isn’t written until you get there.
Does it work for strength training?
Ask for a strength day and you get the real thing: straight sets, the big lifts, proper rest between them. Your weight and reps arrive pre-filled from last time, and logging is one tap. Or switch logging off entirely.
How long are the workouts?
As long as you have. The slider runs from 5 to 90 minutes, and the time you pick is the time it takes. A real 20-minute session beats an imaginary 60-minute one.
Which phones and languages?
iPhone, iPad and Android, in nine languages: English, Spanish, French, German, Italian, Portuguese, Polish, Japanese and Korean.
iOS & Android
Workouts you’ll actually do.
The best workout is the one you just did.
Get Kronos on the App Store or Google Play (listed as Kronos Studio). A workout for the day you’re actually having, ready when you open it.
Free to start. No subscription, no card.
Built for the days you didn’t feel like it.