When can I eat after fasting?
You can eat when your chosen fasting duration has elapsed since your last meal ended. On a 16:8 schedule with a last meal at 8:15 PM, that is 12:15 PM the next day. No other variable changes it. Your age, your weight and the day of the week have no effect on the arithmetic, which is why this fasting time calculator never asks for them.
The formula
Last meal time plus fasting hours equals your eating time. That single line is the whole method behind every fasting time calculator on the internet, including this one. What tools add on top is handling the edge cases correctly rather than any extra cleverness in the sum.
Why your answer lands today or tomorrow
Most fasts cross midnight, so the answer usually falls on the following day. An 8:15 PM last meal plus 16 hours is 12:15 PM tomorrow. A fast that begins after midnight, say a 1 AM finish, ends the same calendar day. Anything past 24 hours lands two days out. This calculator labels every result with the day it falls on, which is the detail hand arithmetic most often gets wrong.
How to calculate your fasting time by hand
Worth knowing, so the result above is something you can check rather than something you have to trust. If the whole fast sits inside one day, subtract. A fast from 6 AM to 4 PM is ten hours. That case is easy and almost nobody gets it wrong.
Counting across midnight
Split the fast at midnight and add the two halves. From an 8 PM dinner, four hours takes you to midnight, and the remaining twelve take you to 12 PM the next day, which is where a 16-hour fast ends. Reverse it to measure a window you already keep: stopping at 9:30 PM and eating at 8 AM is two and a half hours to midnight plus eight after it, so ten and a half hours. Minutes carry differently from hours, so 9:45 PM plus 16 hours is 1:45 PM rather than 1:45 AM.
The mistake that shortens every fast
The clock starts when your last meal ended, not when it started. A dinner that ran from 7:00 PM to 8:15 PM begins a fast at 8:15 PM. People who log the start of the meal quietly shorten every fast by however long they spent eating, which is how two people following the same protocol arrive at different answers and assume one of them is wrong.
Your fasting time from an 8 PM last meal
| Fast length | You can eat at | Matching protocol |
|---|---|---|
| 12 hours | 8:00 AM next day | 12:12 |
| 14 hours | 10:00 AM next day | 14:10 |
| 16 hours | 12:00 PM next day | 16:8 |
| 18 hours | 2:00 PM next day | 18:6 |
| 20 hours | 4:00 PM next day | 20:4 |
| 23 hours | 7:00 PM next day | OMAD |
| 36 hours | 8:00 AM, two days on | Extended (custom) |
Ate at a different time? Use the calculator above; it works with any last-meal time and any duration, then lets you start a timer, share the schedule, print it, or add it to your calendar.
How long is left, and what happens next
Most people asking when they can eat are already partway through the fast, so the number they actually want is how much time remains rather than a clock time to memorise. That is what the timer is for: it counts down live, and it keeps counting if you close the tab.
Your eating window opens, it does not just start
The end of a fast is also the start of something with its own deadline. On a 16:8 schedule the eight hours that follow are when eating happens, and the next fast begins when they close. The calculator returns both boundaries together for that reason, because knowing you can eat at noon is only half an answer if you do not know the window shuts at 8 PM.
If you break the fast early
Then the fast was shorter than planned, and that is the entire consequence. There is no threshold below which a fast stops counting, and any tool suggesting otherwise has invented the rule. Record what actually happened, because a history built from real times is the only one worth having. Over a few weeks your own average is a more useful number than any single day's target.
Looking for Ramadan or Yom Kippur times?
This tool cannot give you those, and it is better to say so than to waste your time. Religious fast times are set by sunset and sunrise for your particular city on a particular date, which is an astronomical calculation. Iftar in Chicago and iftar in Philadelphia are different times on the same evening, and both shift by a minute or two every day.
This fasting time calculator works from a duration instead. You tell it when you stopped eating and how many hours you intend to fast, and it adds them. There is no location in the calculation and no sunset table behind it, so it has nothing useful to say about observance times. A prayer-time service for your own city is the right tool for that, and it will be more accurate than anything a general fasting site could offer.
There is one thing here that may still help. If you keep an intermittent fasting schedule outside a period of religious observance and want to work out how the two fit together, the schedule planner takes any pair of fixed meal times you give it and reports the gap between them, along with the longest fast that fits. You supply the observance times from a source that knows your location, and the planner handles the arithmetic around them.
How many calories break a fast?
There is no officially agreed number, and any page that gives you one with confidence is inventing it. Different researchers and different fasting communities draw the line in different places, commonly somewhere between zero and 50 calories, and no trial has established a single threshold that applies to everyone.
What we can tell you is how this tool treats it, which is the part that affects your schedule. For calculation purposes, a fast ends when you consume anything with meaningful calories. Plain water, black coffee and unsweetened tea are generally treated as compatible with fasting. Anything carrying sugar, milk, cream or oil ends the fast and restarts the clock from that moment.
For a full item-by-item reference with calorie counts, covering coffee, gum, cough drops, electrolytes, oils and the rest, see what breaks a fast. This page stays on the timing question.
From answer to action
Knowing your eating time is step one; remembering it at hour thirteen is the real problem. That is why every result here connects to the rest of the toolkit. "Start fast" launches a live fasting timer that counts down to the exact minute, survives closed tabs, and rolls into your eating window when the fast completes. "Add to calendar" generates events for your fast end and window close. And every completed fast lands in your local history, so over a few weeks you can see your actual average fasting time, which is far more useful than any single day's answer.
If the question underneath yours is what to eat when the window opens, our how to break a fast guide covers the general principles, including the honest point that no trial establishes a best food for breaking a daily fast.
Common timing mistakes
- Counting from bedtime instead of the last bite. The fast starts when eating stops. A 9:30 PM snack after an 8 PM dinner moves your entire window 90 minutes later.
- Rounding across midnight. "About 16 hours from 8-ish" drifts surprisingly far. Exact times keep your tracking honest, and the calculator makes exact effortless.
- Confusing fast length with wake-up time. Your fast ends a fixed number of hours after your last meal, not at a fixed clock time. Eat later, and the end moves later with it, unless you deliberately switch to a fixed eating window, which is what the schedule planner builds.
- Treating a shifted fast as a failed fast. If dinner ran late, the honest response is a later end time rather than abandoning the day. Our timer's "Edit start time" exists precisely for this.