Free until 1 NovStart free

Intermittent fasting, in your browser

Your fast has a temperature.

It measures the hours since you last ate and shows what your body is doing with them. The dial warms as you switch from food to fat. Sal, the salamander who lives in it, sleeps while you digest and glows once you reach ketosis.

Start freeSee the instruments

Free until 1 November 2026 · 40 days left. No card needed. After that, $3.99 a month or $29 a year.

A dial runs a sixteen-hour fast end to end, changing colour as it passes each metabolic phase, while Sal the salamander runs the scale beneath it, stopping at each phase to sleep, wake and glow. All five phases are written out below.

Reading now

Fed

You are still absorbing your last meal. Insulin is up and your body is running on what just arrived.

Sal sleeps while you digest.

Demonstration · sixteen hours in about forty seconds

The price

Free until 1 November 2026.

Every account is free until then, and nothing asks for a card. From 1 November 2026 it is $3.99 a month or $29 a year — the whole app either way, nothing held back behind a tier.

40days left

Start free

What you get

Four instruments. One log.

The dial above is the first. The rest sit one tap away on your phone: water, food and the record of every fast — all reading from the same log, all drawn the same way. Nothing here is a mock-up; these are the app’s own components running on invented readings.

Water
500100015002000250030003500ML

A graduated cylinder. Pour a glass with one press and the level rises toward a target set from your weight and how much you move.

Fuel
Protein
96/140 g−44
Carbs
141/220 g−79
Fat
47/65 g−18

The macro rail. Log food from a catalogue and one bar shows how much you ate and what it was made of, against the marks you are aiming for.

Progress
JunAugMWFMon 29 Jun — 13h 53m, short of goalTue 30 Jun — 14h 47m, short of goalWed 1 Jul — 17h 31m, goal metThu 2 Jul — no fastFri 3 Jul — 14h 13m, short of goalSat 4 Jul — 17h 35m, goal metSun 5 Jul — no fastMon 6 Jul — 16h 51m, goal metTue 7 Jul — 17h 14m, goal metWed 8 Jul — no fastThu 9 Jul — 17h 19m, goal metFri 10 Jul — no fastSat 11 Jul — 17h 9m, goal metSun 12 Jul — no fastMon 13 Jul — 17h 23m, goal metTue 14 Jul — no fastWed 15 Jul — 13h 31m, short of goalThu 16 Jul — 14h 47m, short of goalFri 17 Jul — 16h 38m, goal metSat 18 Jul — no fastSun 19 Jul — no fastMon 20 Jul — 17h 20m, goal metTue 21 Jul — 16h 44m, goal metWed 22 Jul — 13h 31m, short of goalThu 23 Jul — 14h 6m, short of goalFri 24 Jul — 16h 42m, goal metSat 25 Jul — 16h 54m, goal metSun 26 Jul — no fastMon 27 Jul — no fastTue 28 Jul — no fastWed 29 Jul — 14h 28m, short of goalThu 30 Jul — 15h 3m, short of goalFri 31 Jul — 13h 9m, short of goalSat 1 Aug — no fastSun 2 Aug — 15h 17m, short of goalMon 3 Aug — 17h 28m, goal metTue 4 Aug — no fastWed 5 Aug — no fastThu 6 Aug — no fastFri 7 Aug — 13h 36m, short of goalSat 8 Aug — no fastSun 9 Aug — 15h 5m, short of goalMon 10 Aug — 16h 45m, goal metTue 11 Aug — 16h 13m, goal metWed 12 Aug — 16h 20m, goal metThu 13 Aug — 17h 41m, goal metFri 14 Aug — 16h 58m, goal metSat 15 Aug — 16h 17m, goal metSun 16 Aug — 16h 52m, goal metMon 17 Aug — 17h 19m, goal metTue 18 Aug — 17h 34m, goal metWed 19 Aug — 16h 26m, goal metThu 20 Aug — 17h 10m, goal metFri 21 Aug — 16h 43m, goal metSat 22 Aug — 16h 13m, goal metSun 23 Aug — 17h 6m, goal metMon 24 Aug — 16h 38m, goal metTue 25 Aug — 14h 59m, short of goalWed 26 Aug — 16h 59m, goal metThu 27 Aug — 17h 34m, goal metFri 28 Aug — 13h 1m, short of goalSat 29 Aug — no fastSun 30 Aug — 17h 36m, goal metMon 31 Aug — 17h 37m, goal metTue 1 Sept — 16h 15m, goal metWed 2 Sept — 17h 13m, goal met
Days lit
34/66
Longest run
15days
  • Goal met
  • Fast, short of goal
  • No fast

The record. Weigh-ins on a trend line, every finished fast, your streak, and a grid that lights on each day a fast reached its goal.

Coach

Ask Sal about your own numbers.

The coach reads your program, today’s log and your recent fasts before it answers, so you never have to explain what plan you are on. It answers in plain sentences, will not diagnose, and will not invent a figure that is not in your log.

11:52

I'm 14h in and hungry. Push on or eat?

Sal11:52

Push on, if it is ordinary hunger — the kind that comes in a wave and goes when you drink some water and do something else for ten minutes. You are two hours from your 16-hour goal and your window opens at 12:00, so the plan already has you eating soon.

If you feel shaky, light-headed or sick, that is not a wave. End the fast and eat. The goal can wait for another day.

Meet Sal

A salamander lives in your fast.

Folklore had salamanders born in fire. Ours is born at hour zero. Sal sleeps while you digest, wakes when your body turns to stored fuel, runs once fat burning starts, and glows at ketosis — always the same colour as the dial, because it takes its temperature from the same fast.

Sal is also your coach. Ask it anything about your fast, your water or your food, and it answers from your own log.

  1. 00:00FedAsleep
  2. 04:00Post-absorptiveAwake
  3. 12:00Fat burningRunning
  4. 16:00KetosisGlowing
  5. 24:00Deep fastGlowing cold

The sequence

Five stages. Real hours.

The hours are approximate — two people at hour fourteen are not in the same place, and neither is one person on two different days — and the app says so wherever it shows them. It draws them because knowing roughly what is going on is what makes hour fourteen bearable.

Hours into a fast · the face wraps at 24

  1. 00:00

    Fed

    to 04:00

    You are still absorbing your last meal. Insulin is up and your body is running on what just arrived.

  2. 04:00

    Post-absorptive

    to 12:00

    Absorption is finishing. Your body turns to stored glycogen in the liver for its running costs.

  3. 12:00

    Fat burning

    to 16:00

    Liver glycogen is running low, so more of your energy now comes from released body fat.

  4. 16:00

    Ketosis

    to 24:00

    Your liver starts converting fatty acids into ketones, an alternative fuel your brain can use.

  5. 24:00

    Deep fast

    and onwards

    Cellular recycling is thought to step up around here. Long fasts are demanding — go in rested and hydrated.

What the intake produces

Twelve answers in. A schedule out.

One invented person, run through the real builder. The answers are made up; the figures are what the code returns for them, computed on this page by the function that would compute yours.

Her answers
Sex
Female
Age
41
Height
168 cm
Weight
78 kg
Goal weight
70 kg
Activity
Lightly active
Aim
Lose fat
Fasted before
Never
Schedule wanted
16:8
Wakes at
07:00
Rather eat
Around midday
Health flags
None

Her program

16:8

16:8 — The common one. Skip breakfast, eat between midday and evening. You have not fasted before, so the first weeks move your first meal later in steps rather than all at once. 1,610 kcal a day sits about 403 under what you burn.

Eating window

12:00–20:00

She wakes at 07:00 and would rather eat around midday, so the window is anchored to waking rather than to a rule about breakfast.

Every day

1,610kcal

Protein
140 g
Carbs
123 g
Fat
62 g
At rest
1,464 kcal
Maintenance
2,013 kcal
Under maintenance
403 kcal
Water
2.8 L

Mifflin-St Jeor and standard activity multipliers — a population estimate, not a measurement of her. The app calls it a starting setting and expects you to trim it.

Week by week
  1. Week 112:12Week one only moves your first meal later. Nothing else changes.
  2. Week 214:10Push the first meal back another two hours.
  3. Week 316:8Target schedule. Hold here.
If she holds it

0.37 kg a week down, which reaches 70 kg in 22 weeks. That is arithmetic, not a promise — real weight moves in steps and stalls, and the app will not raise the rate past one per cent of body weight a week however hard the answers push.

Position

What you will not find.

No ads.
No screen carries advertising and none is holding a space for it. The app has one job, and it is on the dial.
Nothing sold.
Your fasts, weights and logs live on the one server the app runs on. The only thing that leaves it is the reading the coach needs to answer you, and it is told not to invent a number.
No paywall mid-fast.
There is no phase you upgrade to watch arrive and no prompt between you and the instrument at hour fifteen. Every reading it takes, it shows.
And answers it will not write a plan for
  • Pregnant or breastfeeding
  • Taking insulin or other blood-sugar medication
  • History of an eating disorder
  • Body mass index under 18.5
  • Under 18

Tick any of these in the intake and the builder returns a referral instead of a schedule — nothing generated, nothing saved, and a plain instruction to talk to a doctor or a dietitian first. There is a floor under the daily calorie target for the same reason: if your answers work out below it, the app raises the figure and says so.

Start

Free until 1 November 2026.

Twelve questions across body, habits, hours and health, then you see the whole plan — window, ramp, calories, macros, water — before a single row is written. Every part of it can be changed later from settings.

Now

Free

Until 1 November 2026. No card, no trial timer.

Monthly

$3.99/ month

From 1 November 2026.

Yearly

$29/ year

From 1 November 2026. 39% less than paying monthly.

Start free

Already have an account? Sign in.