Fasting Planner
Pick a protocol, plan your eating window, and track your fast in real time
This tool is for informational and educational use only. It is not medical advice. Intermittent fasting is not safe for everyone — including people who are pregnant or breastfeeding, under 18, underweight, have diabetes, take blood-glucose-lowering medication, or have a history of disordered eating. Talk to a qualified healthcare professional before starting a fasting regimen.
Choose a Fasting Protocol
Fast Start Time
Fasting Stages — What Happens in Your Body
Fed state
Insulin is high, glucose is being used and stored.
Post-absorptive
Digestion winds down; the body finishes processing the last meal.
Glycogen burning
Liver glycogen is the main fuel source. Insulin starts to fall.
Metabolic shift
Glycogen runs low; fat-burning (lipolysis) picks up. Mild ketosis may begin.
Fat burning
Increased fat oxidation. Growth hormone rises.
Mild ketosis
Ketone bodies rise as the body adapts to using fat.
Autophagy ramps up
Cellular "cleanup" processes increase. Glucose levels low and stable.
Deep ketosis
High ketone levels. Significant fat metabolism. Consult a clinician.
Extended fast
Marked autophagy and immune cell turnover. Medical supervision recommended.
Timings are typical averages from physiology literature. Individual response varies with metabolism, last meal composition, exercise, hydration, and medications.
About the Fasting Planner
The Fasting Planner helps you choose an intermittent-fasting protocol, calculates when your fast ends and your eating window opens, and tracks your active fast with a live countdown and stage-by-stage timeline of what's happening in your body.
- 8 protocols: 12:12, 14:10, 16:8, 18:6, 20:4, OMAD (23:1), 24-hour, and 36-hour
- Live timer with progress bar and seconds-precision countdown
- Stage timeline based on fasting physiology (glycogen depletion, mild ketosis, autophagy, deep ketosis)
- Highlights the stage you're currently in and what's next
- Saves the active fast to your browser so you can close the tab and come back
- All times shown in your local timezone — no account, no tracking, no cloud sync
How to Use the Fasting Planner
- 1
Pick a protocol
Click one of the protocol cards. If you're new to intermittent fasting, start with 12:12 or 14:10 — they're labelled Beginner. 16:8 is the most popular intermediate option.
- 2
Set your start time
The fields auto-fill with your current local date and time. Adjust them if you want to plan a fast that starts later — for example, immediately after dinner tonight.
- 3
Review the plan
The purple plan card shows your fast start, fast end, and the eating window that follows. Use this to schedule your meals.
- 4
Start the fast
Click Start fasting now when you finish your last meal, or Use planned start time if you've already entered a specific moment in the past or future.
- 5
Check progress any time
Come back to this page during the day. The active-fast card shows percent complete, time elapsed, time remaining, and which fasting stage you're currently in.
- 6
Break the fast
When the timer hits 100%, eat. If you need to stop early, click End fast. Either way, the timer resets and you can start a new plan.
Tip: Drink water, plain tea, or black coffee during the fast. They keep hunger manageable and won't break a fast for most goals. Watch out for sweeteners, milk, and broths — they re-trigger an insulin response.
Common Use Cases
Weight Management
- • Build a daily 8-hour eating window to reduce overall calorie intake
- • Pair 16:8 with the Calorie Tracker for a steady deficit
- • Use OMAD occasionally to break weight-loss plateaus
Metabolic Health
- • Lower fasting insulin with consistent overnight fasts
- • Reduce post-prandial glucose spikes by fewer meals per day
- • Track timing against blood-sugar and blood-pressure logs
Productivity & Focus
- • Skip breakfast prep and use morning hours for deep work
- • Avoid post-lunch energy crashes by delaying your first meal
- • Schedule meetings inside your eating window
Athletic Training
- • Schedule workouts toward the end of the fast for fat oxidation
- • Time the eating window to capture post-workout recovery meals
- • Use 14:10 on heavy training days, 16:8 on rest days
Religious & Cultural Fasts
- • Plan suhoor and iftar timing during Ramadan
- • Track Lent or other prolonged-fast traditions
- • Build sustainable spiritual-fasting schedules
Habit Building
- • Stop late-night snacking with a fixed kitchen-closed time
- • Train delayed gratification with progressively longer fasts
- • Pair with the Habit Tracker to log streaks
Frequently Asked Questions
Is intermittent fasting safe?
For most healthy adults, short daily fasts (12–16 hours) are well-tolerated. Longer fasts (24h+) carry more risk, especially without supervision. Fasting is not recommended if you are pregnant or breastfeeding, under 18, underweight or recovering from an eating disorder, have type 1 diabetes, take medication that lowers blood glucose, or have a history of fainting. Always speak with a clinician before starting.
What's the difference between 16:8 and OMAD?
16:8 means a 16-hour fast and an 8-hour eating window — typically 2–3 meals. OMAD (One Meal A Day, sometimes written 23:1) compresses all of your daily food into a single ~1-hour window. OMAD is more restrictive, easier to mess up nutritionally, and harder to sustain long-term.
What can I drink during a fast?
Water, sparkling water, plain black coffee, and plain tea are widely considered fast-friendly. Adding milk, cream, sugar, honey, sweeteners, broths, or supplement powders may break a fast depending on your goal — even small calorie or insulin signals can interrupt autophagy and ketosis. Stick to zero-calorie, unflavoured drinks if you want the strictest version.
When does autophagy start?
Autophagy — the cellular "cleanup" process — exists at low levels all the time and is upregulated during fasting. Most physiology evidence suggests meaningful upregulation appears after ~24 hours of fasting in humans, with peak effects much later. The 16–18h "autophagy window" claim often seen online is more aggressive than the data supports.
Will fasting put me in starvation mode?
No. Short-term fasts actually raise metabolic rate slightly (via norepinephrine) for the first 48–72 hours. Metabolic slowdown is associated with prolonged calorie restriction, not short fasts. That said, chronically eating too little — fasting or not — does suppress metabolism, so use this tool with a sensible total calorie target.
Should I break my fast with anything specific?
Start with a small, easy-to-digest meal — protein with vegetables, or a balanced bowl. Avoid breaking a long fast with a huge, refined-carb meal: it can spike blood sugar and cause re-feeding discomfort. For fasts under 24h, normal meals are usually fine.
Can I exercise while fasting?
Yes — many people do fasted cardio or light resistance training without problems. For high-intensity sessions or anything over 60 minutes, schedule training near the end of the fast or inside the eating window, and make sure you're hydrated and electrolyte-replete.
What if I get headaches or feel dizzy?
Mild headaches or light-headedness in the first few days are common and often resolve with water and electrolytes (sodium especially). If symptoms are severe, persistent, or include fainting, confusion, or rapid heartbeat — stop the fast and seek medical advice.
Does this app send my data anywhere?
No. The active fast is stored in your browser's localStorage. Nothing is sent to a server, no account is required, and clearing your browser data will remove the stored fast.
Why does the timer keep running if I close the tab?
The timer doesn't actually "run" — it computes elapsed and remaining time from the start timestamp you saved, on every page load. So closing the tab, putting your phone to sleep, or losing wifi has no effect: when you re-open the page, the numbers are accurate to the second.