If you are asking what time does a 16hour fast end, the direct answer is: it ends 16 hours after the fast begins. For example, a fast that starts at 8:00 pm ends at 12:00 noon the following day. The exact time depends entirely on your chosen fasting start time.
In a typical 16:8 schedule, the 16-hour fast is followed by an 8-hour eating window. Clock-time calculations can help you plan the schedule, but they do not determine whether a particular fasting routine is medically suitable or nutritionally adequate for you.
What time does a 16hour fast end? Common start-time examples
To find the end time, add 16 hours to the time you begin fasting. Most evening start times produce an end time on the following day.
| Fasting start time | 16-hour fast ends | Possible 8-hour eating window |
|---|---|---|
| 4:00 pm | 8:00 am next day | 8:00 am to 4:00 pm |
| 5:00 pm | 9:00 am next day | 9:00 am to 5:00 pm |
| 6:00 pm | 10:00 am next day | 10:00 am to 6:00 pm |
| 7:00 pm | 11:00 am next day | 11:00 am to 7:00 pm |
| 8:00 pm | 12:00 noon next day | 12:00 noon to 8:00 pm |
| 9:00 pm | 1:00 pm next day | 1:00 pm to 9:00 pm |
| 10:00 pm | 2:00 pm next day | 2:00 pm to 10:00 pm |
| 12:00 midnight | 4:00 pm the same calendar day | 4:00 pm to 12:00 midnight |
These are planning examples. Your actual fast starts when you finish the intake that you count as ending your eating window, not necessarily when dinner is served or when you first sit down to eat.
How to calculate your fasting start and end time
The calculation is simple: add 16 hours to the fasting start time. One way to do this is to add 12 hours first and then add another 4 hours.
- Identify when your eating window ends.
- Use that clock time as the beginning of the fast.
- Add 16 hours.
- Treat the resulting time as the start of the next eating window.
For example, suppose you finish your eating window at 7:30 pm. Adding 12 hours takes you to 7:30 am the next day, and adding another 4 hours gives an end time of 11:30 am.
If you want to eat again at a particular time, calculate backwards instead. To begin eating at 10:00 am after a 16-hour fast, count back 16 hours. The fast would need to begin at 6:00 pm on the previous day.
How a 16:8 eating window fits into the schedule
A 16:8 schedule divides a 24-hour day into a 16-hour fasting period and an 8-hour eating window. The durations add up to 24 hours:
- Fasting duration: 16 hours
- Eating duration: 8 hours
- Total schedule: 24 hours
For a practical scenario, consider someone who prefers lunch at noon and wants an 8-hour eating window. Their window could run from 12:00 noon to 8:00 pm. The next 16-hour fast would run from 8:00 pm until 12:00 noon the following day.
The sequence is continuous. The eating window ends when the fast starts, and the fast ends when the next eating window begins. Any delay in starting the next eating window makes the fast longer, while beginning earlier makes it shorter.
Understanding midnight and next-day times
Fasting calculations often cross midnight, which can make the answer seem less obvious. The date changes at midnight, but the hours continue normally.
For example, a fast beginning at 9:00 pm has three hours remaining until midnight. Another 13 hours are then needed to complete 16 hours, so the fast ends at 1:00 pm the next day.
Take extra care with 12:00 am and 12:00 pm:
- 12:00 am means midnight.
- 12:00 pm means noon.
- A fast from 8:00 pm to 12:00 pm lasts 16 hours.
- A fast from 8:00 am to 12:00 am also lasts 16 hours.
Using a 24-hour clock can reduce ambiguity. For example, 8:00 pm is 20:00, while noon is 12:00. A fast from 20:00 to 12:00 the next day is 16 hours.
What a fasting window calculator can and cannot tell you
A fasting window calculator handles the clock arithmetic for you. It can convert a chosen eating duration into a fasting duration and estimate when the next eating window starts.
The basic method is:
- Eating-window end time = eating-window start time + eating duration
- Fasting duration = 24 hours − eating duration
For example, an eating window beginning at 12:00 noon and lasting 8 hours ends at 8:00 pm. That leaves a 16-hour fasting window, ending at 12:00 noon the next day.
What the calculator can estimate
- Your planned fasting duration
- Your planned eating-window duration
- The clock time when the eating window ends
- The estimated start of the next eating window
- Schedules that cross midnight
What the calculator cannot establish
- Whether a fasting schedule is suitable for your health circumstances
- Whether the foods eaten provide adequate nutrition
- Whether you followed the planned times exactly
- How your body will respond to a particular schedule
- Whether the schedule will change your weight
The output is a schedule estimate rather than a measurement of what occurred. If the planned fast starts at 8:00 pm but your actual eating window ends at 8:20 pm, a full 16-hour period would end at 12:20 pm the next day.
Choosing a practical eating window
The most convenient schedule varies according to work, sleep, family meals, travel and personal routines. Rather than choosing an end time in isolation, consider both ends of the eating window.
For example, a 10:00 am to 6:00 pm eating window may suit someone who prefers an early dinner. A 12:00 noon to 8:00 pm window may fit a later family meal. Both leave a 16-hour period outside the eating window.
Consistency in clock times can make planning simpler, but a calculated schedule does not need to be treated as proof of adherence. Record the actual time the eating window ended if you need an accurate end-time calculation for that day.
Frequently asked questions
If I stop eating at 8:00 pm, when does a 16-hour fast end?
It ends at 12:00 noon the following day. The corresponding 8-hour eating window could run from noon until 8:00 pm.
If I want to eat at 9:00 am, when should the fast begin?
Count back 16 hours from 9:00 am. The fast would begin at 5:00 pm on the previous day.
Does the fasting period begin at the start or end of dinner?
For schedule calculations, it begins when your eating window ends. If dinner starts at 7:00 pm but finishes at 7:45 pm, using 7:45 pm as the start produces an end time of 11:45 am the next day.
Can a 16-hour fast begin in the morning?
Yes. A fast beginning at 8:00 am ends at midnight. Although evening-to-daytime schedules are common examples, the arithmetic works from any starting time.
What happens if I start eating earlier than planned?
The completed fast is shorter than the planned 16 hours. For example, a fast beginning at 8:00 pm and ending at 11:30 am lasts 15 hours and 30 minutes, not 16 hours.
Is a 16-hour fast the same as an 8-hour eating window?
They are complementary parts of a 24-hour schedule. A 16-hour fasting period leaves an 8-hour eating window, provided the schedule repeats over 24 hours.
Summary
The answer to what time does a 16hour fast end depends on when the fast starts. Add 16 hours to the end of your eating window: an 8:00 pm start ends at noon the next day, while a 6:00 pm start ends at 10:00 am.
A fasting window calculator can make these time conversions easier, especially when a schedule crosses midnight. Its result is a planning estimate based on the times entered, not an assessment of health suitability, nutritional quality or likely weight change.