16:8 vs 18:6 vs 20:4: Which Intermittent Fasting Schedule Should You Choose
All three are time-restricted eating schedules, named for the fasting hours to eating hours split. 16:8 means 16 hours fasting and an 8 hour eating window. 18:6 tightens that to 6 hours of eating. 20:4 narrows it further, to a single 4 hour window. None of them are inherently "better," they're different levels of restriction, and the right one depends on your schedule, your appetite, and how your body responds.
What the research actually shows
Harvard's School of Public Health notes that daily time-restricted eating with at least 16 hours of fasting has been associated with weight loss roughly equivalent to a 250-calorie-a-day deficit, or about half a pound a week (Harvard T.H. Chan School of Public Health). That is a meaningful but modest effect, not a dramatic one.
It is also worth being honest about the limits of the evidence. A widely covered one-year randomized trial found that 16:8 time-restricted eating was not more effective for weight loss than simple calorie reduction without a restricted eating window (Smithsonian Magazine). If you've seen fasting marketed as a metabolic shortcut, that claim deserves more skepticism than it usually gets.
Harvard Health also points to timing, not just duration, as a factor: eating windows that end earlier in the day, by around 6pm, have been linked to better blood sugar and blood pressure outcomes than the same fasting window shifted later (Harvard Health).
Choosing where to start
Harvard Health's own suggestion is to ease in rather than jump to the tightest schedule: start with a 12:12 split, where you eat across 12 hours and fast for 12, before narrowing the window further. That gradual approach is easier to sustain and easier to notice how your body reacts.
A rough way to think about the three:
16:8 is the most sustainable for most people. An 8 hour window still fits a normal breakfast-to-dinner routine for many schedules, or a lunch-to-dinner window if you prefer to skip breakfast.
18:6 suits people who are already comfortable with 16:8 and want to push further, typically by skipping one meal entirely rather than compressing all three into a tight window.
20:4 is the most restrictive of the three, usually one larger meal plus a small additional eating occasion. It is harder to sustain long-term and worth approaching cautiously, especially if you have any underlying health condition.
Tracking it without trading your data for it
Whichever schedule you choose, a timer that just tells you when your window opens and closes is the entire feature set you need. It does not need an account, a login, or a connection to the internet to do that job.
FasTrack supports 16:8, 18:6, 20:4, and fully custom schedules, runs entirely offline, and does not require an account. It is built to be the timer, not a thing that builds a profile of your eating habits in the background.
This article is for general information and is not medical advice. Fasting is not appropriate for everyone, including people with certain medical conditions, a history of disordered eating, or who are pregnant or breastfeeding. Talk to a healthcare professional before starting any fasting schedule.