16:8 Fasting Schedule Planner & Timer

Fast for 16 hours and eat within 8: set the time your last meal ends and see when to break your fast, when your eating window closes and the body stages along the way. Start the live 16-hour timer when you're ready.

100% private: runs in your browser, nothing is uploaded

Choose your fasting plan

My last meal ends at

Fast begins: 8:00 PM
Window opener meal: 12:00 PM next day
Eating window: 8 hours
Window closer meal: 8:00 PM next day

Cellular Renewal & Body Insights Timeline

1
0–4h · from 8:00 PM
Blood Sugar & Insulin Stabilization
Your last meal is being digested. Blood sugar rises, then insulin brings it back to a steady level.
2
4–12h · from 12:00 AM next day
Glycogen Depletion & Digestive Rest
Insulin falls and your body draws on the sugar stored in your liver (glycogen) while digestion rests.
3
12–16h · from 8:00 AM next day
Fat Burning & Metabolic Switch
With glycogen running low, your body turns increasingly to stored fat for fuel.
4
16h+ · from 12:00 PM next day
Mild Ketosis & Cellular Renewal (Autophagy)
Ketone levels rise. Research suggests autophagy, the body’s recycling of worn-out cell parts, steps up with longer fasts.

Timings are typical averages and vary with your last meal, activity and metabolism.

Live fasting timer

Keeps counting even if you close this tab. Saved on this device only.

JaxFit gives general wellness information, not medical advice. Talk to a doctor before fasting or changing your diet if you are pregnant or breastfeeding, have diabetes or another medical condition, take regular medication, or have a history of eating disorders.

JaxFit: Fasting & Weight Loss

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Guide

A Simple 16:8 Day

The classic 16:8 day: finish dinner by 8 PM, sleep, have water, black coffee or plain tea in the morning, and eat your first meal at noon. Your eating window then runs from noon to 8 PM, with two or three meals or a meal and a snack.

Prefer an earlier window? Finish eating at 6 PM and break your fast at 10 AM. Any eight-hour window works: pick the one that fits your work, family meals and sleep, and keep it roughly the same each day.

Break your fast with protein, vegetables and some healthy fat rather than a large, sugary meal, and eat enough across your window. If 16 hours is too long at first, begin with 14:10 and add an hour every week or so.

Step by step

How to Use the JaxFit Calculator

1
Enter your details
Height, weight, age and activity, in metric or imperial. They're saved on this device for next time.
2
Plan your fasting window
Pick 14:10, 16:8, 18:6, 20:4, 24h or your own plan and the time your last meal ends.
3
Check your numbers
See your WHO BMI, healthy weight range, safe calorie target, goal date and daily water.
4
Grow your Habit Garden
Start the live fasting timer, log water and healthy meals, and watch your plant flourish.

Private by design

Your Health Data Stays on Your Device

Every calculation runs in your browser. Nothing you enter is uploaded or sent anywhere.
No accounts, no analytics cookies, no tracking scripts and no ads.
Your details, timer and garden are saved only on this device. Clearing your browser data removes them.

FAQ

Frequently Asked Questions

How do I start a 16:8 fasting schedule?

Pick the time your last meal usually ends, for example 8 PM. Your fast then runs until 12 noon the next day, and you eat between noon and 8 PM. Sleep covers about half the fast. Water, black coffee and plain tea are fine while fasting. If 16 hours feels hard, start with 14:10 for a week or two and move the first meal later by 30 minutes at a time.

What is the difference between 16:8 and 18:6 intermittent fasting?

Both are daily time-restricted eating plans. On 16:8 you fast for 16 hours and eat within an 8-hour window, for example noon to 8 PM. On 18:6 you fast for 18 hours and eat within 6 hours, for example 2 PM to 8 PM. 16:8 is the most popular starting point because it mostly uses the hours you are asleep. 18:6 adds two more hours in the fat-burning stage, but it is harder to keep up, so most people build up to it gradually from 14:10 or 16:8.

What should I eat to break a fast?

Open your eating window with a balanced, gentle meal: some protein (eggs, yoghurt, lentils, fish or chicken), fibre-rich vegetables or fruit, and a source of healthy fat. Avoid breaking a long fast with a very large or very sugary meal. Drinking a glass of water first helps too. Within your window, aim to eat enough overall: fasting is about when you eat, not about eating as little as possible.

What happens to your body during a fast, hour by hour?

In the first 0–4 hours your last meal is digested and insulin brings blood sugar back to a steady level. From about 4–12 hours insulin falls and your body uses the sugar stored in your liver (glycogen) while digestion rests. Around 12–16 hours glycogen runs low and your body switches more to burning stored fat. After about 16 hours ketone levels rise (mild ketosis) and research suggests autophagy, the body's recycling of worn-out cell parts, increases. These timings are typical averages: your meals, activity and metabolism shift them.

Who should not try intermittent fasting?

Intermittent fasting isn't suitable for children and teenagers, during pregnancy or breastfeeding, for people with a history of eating disorders, or for anyone underweight. If you have diabetes, take medicines that lower blood sugar or blood pressure, or have another medical condition, talk to your doctor before you start. Stop and eat if you feel dizzy, faint or unwell.

Is my health data private on JaxFit?

Yes. Every calculation runs in your own browser. Your age, weight, goals, fasting timer and Habit Garden are saved only in your browser's local storage on this device, so they're there when you come back. Nothing is uploaded, there are no accounts, no analytics cookies, no tracking scripts and no ads. Clearing your browser data removes everything.