How to start intermittent fasting: a two-week ramp

Intermittent fasting is an eating schedule that makes the stretch between your last meal and your first meal longer. To start, pick a daily schedule such as 12:12, 14:10 or 16:8 (fasting hours first, eating hours second) and build up by moving only your first meal later. The two-week ramp below goes 12:12, then 14:10, then 16:8.

Talk to a doctor first if any of this applies to you. Harvard Health says a time-restricted eating approach "appears to be a safe strategy" for most people, "with notable exclusions of those who have diabetes, eating disorders, are pregnant or breastfeeding, or require food with their meds." Fasting Timer's own note in Settings adds under 18 and "a medical condition" to pregnancy and diabetes. If you're in one of these groups, or you aren't sure, ask before you start.

What intermittent fasting means

Harvard Health calls intermittent fasting "a catch-all term for one of the key levers in our dietary pattern: timing," and defines it more exactly as "an eating schedule that is designed to expand the amount of time your body experiences a fasted state." You get there "by reducing the so-called eating window." The schedules in this guide are all daily ones, so they split a 24-hour day.

The ramp below keeps your last meal where it is and only moves the first one later.

The two-week ramp

This is one way to lay out the first two weeks, built on plain arithmetic. It isn't a medical protocol, and the Harvard article doesn't say how long to stay on each step. Every day uses the same last bite at 8 pm, so only the morning changes.

Swap 8 pm for your own last bite. The first meal is always that time plus the fasting hours: a 7 pm last bite on 14:10 means a 9 am first meal.

A few ways to bend it to your life:

• Repeat a step. If a step doesn't fit your week, stay on it for a few more days before moving to the next one.
• Start where you already are. If dinner ends at 8 pm and breakfast is at 8 am, you're already on 12:12, so you can begin the table at day 5.
• Plan around real meals. An 8-hour window has to hold the meals you eat with other people. If a standing lunch at 11:30 doesn't fit a noon start, use 14:10 on those days.

What to expect from the research

Harvard Health's article covers a yearlong randomized trial of time-restricted eating with calorie restriction (Liu et al., N Engl J Med 2022) in adults aged 18 to 75 with a BMI between 28 and 45; 118 completed it. The time-restricted group ate its prescribed calories within eight hours, the comparison group followed the same calorie reduction without a time limit. Both lost weight, about 18 pounds and 14 pounds, and the difference wasn't statistically significant. The author concludes that "restricting the eating window alone does not have a substantive impact on weight loss."

That is one trial in a specific group, and both arms cut calories, so it can't tell you what happens in the first two weeks or for people outside that BMI range. Harvard also notes the wider evidence often comes from "very small sample sizes, short intervention periods" and varied study designs. Harvard adds that if you overcompensate "by gorging yourself during your eating window, it will not work as a weight loss strategy," and that the quantity and quality of what you eat "still matter immensely."

Running the ramp in Fasting Timer

Fasting Timer is an iPhone app (iOS 17 or later). The daily plans, 12:12, 14:10, 16:8, 18:6, 20:4 and OMAD, are free. Fasts of 24, 36 and 48 hours and custom fasts from 1 to 72 hours are Premium.

On first launch the onboarding asks "Have you fasted before?", with the line "No wrong answers. You can change your plan anytime." Choose "I'm new to fasting" and the next screen, "Your starting plan", marks 12:12 with "For you". The screen says "Recommended for you. Start easy and build up." That's the app's own suggestion, not medical guidance, and it matches where the table above starts.

Then, for each step of the ramp:

1. Open the Timer tab and tap the plan chip at the top. It shows the current plan and its tagline, for example "12:12 · A gentle start".
2. In Choose a plan, tap a card under Daily plans. 12:12 is "A gentle start", 14:10 is "Easy daily rhythm" and 16:8 is "Most popular". Choosing one closes the list.
3. The ring shows "Ready to fast" with your plan and its hours. Tap Start fasting when you finish your last meal.
4. The Started and Goal boxes show when you began and when the fast ends. The Goal time is your first meal in the table.
5. Started later than you tapped? Tap Started to open Edit start time, set the real time and tap Save.
6. Once the goal is reached the button reads Complete fast. Before that it reads End fast.

The app sends a notification when the fast is complete and one an hour before it ends. The free version keeps your last 7 days and current streak. Fasting Timer doesn't count calories, give meal plans or sync across devices; your data stays on your iPhone.

After week two

16:8 is the end of this ramp. To go deeper into it, see the 16/8 fasting guide for start times and a week-one example. To compare every daily schedule, there is the intermittent fasting schedule table. For what to drink during the fast, read coffee while fasting. For what the app's stages show at each hour, see fasting stages, and if hunger is the hard part, read does hunger go away when fasting.

Fasting stages are general information, not medical advice. Talk to your doctor before fasting, especially if you are pregnant, have diabetes or another medical condition.