Home Screen widgets
Elapsed time, goal, protocol and streak, in small or medium size.
Intermittent fasting · iPhone and Apple Watch
Your fast, on an honest clock.
Fastii times your 16:8, 18:6 or OMAD in one tap, keeps your streak, and tells you when your eating window opens. No miracle diets, no account, no ads.
- 24-hour free try
- No account
- Your data stays on your iPhone
How it works
Three steps. Zero friction.
Fastii is for people who already decided to fast and just want a clear clock that stays out of the way.
- 1
Pick your schedule
14:10 to ease in, 16:8 the classic, 18:6, 20:4, OMAD, or your own split. Three questions and you’re set.
- 2
Tap start
The clock runs on your iPhone, your Home Screen widget and your Apple Watch. Started an hour ago? Set the real start time.
- 3
End it and add it up
Note how it felt and how many glasses of water you had. The fast lands in your history and your streak goes up.
Intermittent fasting calculator
When do you eat, and when do you fast?
Pick a protocol and the time you start fasting. We’ll show your eating window on a 24-hour clock, just like the app.
- Fast
- 8:00 PM → 12:00 PM16 hours
- Eating window
- 12:00 PM → 8:00 PM8 hours
16:8fast · eat
- Fast
- Eat
- 4h marks
An informational planning tool. Not medical advice.
Inside the app
Everything you need. Nothing you don’t.
Always in view
Without opening the app, you know what’s left.
Apple Watch
Check your fast from your wrist, with your goal and streak.
Alerts you choose
Window opens, window closes, goal reached, and clock marks. Scheduled on your iPhone.
Features
Fasting essentials, done right.
Live circular clock
Hours, minutes and seconds, with your goal and time left always in view.
4, 8, 12 and 16h marks
Dots on the clock to pace the way. They’re time marks, not claims about your body.
History and calendar
Every fast with its start time, length and how it went. Add or fix past fasts.
Current and best streak
Days in a row, weekly hours, average length and your longest fast.
Water during a fast
Add glasses with one tap and get an optional water reminder.
Optional weight and waist
A trend chart in kg or lb. A number over time, with no promise to lose.
Local alerts
When your window opens or closes, at your goal and at each mark, if you turn them on.
Light and dark mode
Follows your iPhone’s appearance. In English or Spanish, your choice.
No fine print
A clock, not a promise.
Plenty of fasting apps sell you magic stages and guaranteed results. Fastii does one thing: time your fast clearly and respect your privacy.
What Fastii does
- Times your fast, to the second
- Keeps your history and streak
- Tells you when your window opens or closes
- Works offline, with no account and no ads
What Fastii doesn’t do
- Promise fat burning or weight loss
- Invent ketosis or autophagy “stages” on the clock
- Sell you a diet plan or recipes
- Upload your data to any server
Read the privacy policy. It’s short and written for people.
Pricing
Try it for 24 hours. Decide later.
Download Fastii, set your schedule, and use the timer, history and streak for a full day. If it works for you, keep going with Fastii Plus.
Fastii PlusYearly or monthly
- Fasting timer with every protocol
- Unlimited history, calendar and streak
- Widgets and Apple Watch app
- Water, weight, waist and alerts
Price in your currency is shown before you pay. Renews automatically; cancel anytime in your Apple ID settings.
Is Fastii free?
It’s free to download. After setup you get 24 hours to use the timer, history and streak without paying. To keep using them you need Fastii Plus, a yearly or monthly subscription. The price in your currency is shown before you pay, and you can cancel anytime in your Apple ID settings.
Which fasting protocols are included?
14:10, 16:8, 18:6, 20:4, OMAD (one meal a day), and a custom schedule with 12 to 23 hours of fasting. You can switch protocols anytime.
Do I need an account?
No. Fastii has no accounts or sign-in. Open the app, answer three questions, and start your first fast.
Where is my data stored?
On your iPhone. Your fasts, notes, water and weight never leave the phone. We don’t use analytics or ads. Purchases are processed by Apple and validated by RevenueCat with an anonymous identifier, never your fasting log.
Does it work with Apple Watch?
Yes. Apple Watch shows your fasting time, goal and streak. There are also Home Screen widgets for iPhone.
Does Fastii tell me what to eat or how much I’ll lose?
No. Fastii is an informational timer and log. It is not a medical device, does not diagnose or treat any condition, and does not prescribe a diet. If you are pregnant, breastfeeding, have diabetes, take medication, or have a history of disordered eating, talk to a health professional before fasting.
From the blog
Intermittent fasting, plainly.
Habits
How to stick with intermittent fasting: streaks, bad days and consistency
Why most people quit intermittent fasting in the first few weeks, and seven practical ideas to turn it into a habit that lasts for months.
ProtocolsOMAD: what eating one meal a day means, and who it isn’t for
What OMAD (one meal a day) is, how it differs from 20:4 and 16:8, how a day is organized, and why it’s not the best starting point for most people.
Common questionsWhat breaks a fast? Water, coffee, tea, gum and more
A practical guide to which drinks and products are usually fine during intermittent fasting and which count as food, with honest nuance where there’s no consensus.
Your next fast starts with one tap.
Download Fastii and try it free for 24 hours.
Download on theApp Store