Fasting Clock

Track water-only or assisted fasts from 16 hours toward longer windows. The clock shows educational stage labels based on hours without food. It does not diagnose, supervise, or prove biological processes occurred.

How to use this

  1. Choose water-only or assisted fasting and pick your goal hours.
  2. Tap Start fast when you finish your last bite. When you reach your goal, we show how to break the fast with meal ideas.
  3. Stage labels mark educational time windows only — they do not prove biological processes occurred.
Fasting type
Goal duration

Optional: Dr. Boz Ratio (glucose ÷ ketones)

Formula: glucose (mg/dL) ÷ ketones (mmol/L). Interpretations are educational only — not diagnostic targets. See our ratio guide for limitations.

Breaking intermittent fast (≤18h)

Shorter fasts (16:8, 18:6) are the easiest to break. A balanced low-carb meal with protein, healthy fat, and fiber is a common starting point.

How to break your fast

  1. 1Open your eating window with a balanced low-carb meal — not snacks or grazing.
  2. 2Prioritize protein (eggs, chicken, fish, cottage cheese) plus healthy fat.
  3. 3Add non-starchy vegetables or a small side of greens for fiber.
  4. 4Eat when hungry, stop when full — your first meal after IF is not an excuse to overeat.
  5. 5Stay low carb if that matches your eating plan.

What to avoid

  • • Breaking with toast, oatmeal, or cereal if you are following a low-carb plan.
  • • Sweetened coffee drinks or "keto" bars loaded with sugar alcohols as your first bite.
  • • Skipping protein and eating only nuts or cheese — balance matters.

Tips

  • 16-hour fasts are a common entry point for time-restricted eating — break them with real food: protein, fat, and fiber.
  • On lower-carb eating, hunger often stays moderate — your first meal can be lunch-sized. No need to "make up" missed calories.
  • Optional Dr. Boz Ratio tracking after eating is for personal observation only; it is not a treatment target.

Suggested break-fast meals

All recipes

Read the full break-fast guide →

Not medical advice. This timer tracks clock time only. Talk to your doctor before fasting — especially on diabetes, blood pressure, or kidney medications. Do not adjust medication on your own.

Fasting timer

Ready to start

00:00:00

Set your goal and tap Start fast. Your timer persists if you close the tab.

Assisted vs water-only fasting

Water-only is the strictest — plain water only. Assisted adds electrolytes, bouillon for sodium, and black coffee or tea without calories. Both avoid caloric food and sweeteners that break a fast.

Compare modes in our water fast vs assisted fast guide. Most people tolerate assisted plans better past 24 hours because sodium replacement is explicit.

Safety before longer fasts

Extended fasts affect blood sugar and blood pressure — especially on diabetes or BP medication. Read fasting on diabetes medications and electrolytes during fasting before going past 24 hours.

Plan the exit as carefully as the start: how to break a 24-hour fast and best first meal after fasting.

Related timers

Prefer a named IF schedule? Use the intermittent fasting timer. Planning 36–72 hours with clearance? Open the extended fasting clock. Strict plain-water only? See the water fast timer.

Related guides

Fasting

How to Break a 24-Hour Fast Safely

General meal-planning considerations after a 24-hour fast, including symptoms that require medical help.

9 min read

Fasting clock →

Fasting

16:8 vs 18:6 Intermittent Fasting — Which Is Right for You?

Compare 16-hour and 18-hour eating windows, the limits of current evidence, and situations that require clinical advice.

9 min read

IF timer →

Fasting

Electrolytes During Fasting — Sodium, Potassium & Magnesium

What sodium, potassium, and magnesium do, why symptoms are nonspecific, and when supplements can be unsafe.

11 min read

Extended fasting clock →

Frequently asked questions

What is assisted fasting vs water-only?

Water-only means plain water — strictest, best for shorter fasts. Assisted adds zero-calorie electrolytes, bouillon/broth, and black coffee or tea without calories. Both avoid caloric food and drinks.

When does autophagy start?

Human autophagy timing is uncertain and cannot be measured at home. Some research discusses cellular cleanup after many hours without food, but a timer cannot confirm it. See our guides for limitations.

Is extended fasting safe?

Fasts beyond 24 hours carry electrolyte and refeeding risks — especially on diabetes or blood pressure medications. Always consult your doctor before extended fasting. Do not adjust medication on your own.

Other calculators

Metabolic Low Carb Calculator · https://metaboliclowcarb.com