acalculator

When does my fast end?

Enter the day and time of your last meal and how many hours you want to fast. See when the fast ends and, for daily plans such as 16:8, when your eating window closes.

Your numbers

Your fast ends
Thursday, October 1, 2026, 12:00 PM

A 16-hour fast that starts at 8:00 PM on September 30, 2026 ends on Thursday, October 1, 2026, 12:00 PM.

End date
October 1, 2026
End time
12:00 PM
Eating window
8 hours
Eating window closes
Thursday, October 1, 2026, 8:00 PM
Fast length in minutes
960

Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.

Your fast ends: Thursday, October 1, 2026, 12:00 PM. A 16-hour fast that starts at 8:00 PM on September 30, 2026 ends on Thursday, October 1, 2026, 12:00 PM.

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Works out when a fast ends from its start time and length, and for daily intermittent fasting such as 16:8 the eating window that follows.

Example with the default inputs (Fast starts on September 30, 2026, At 20:00, Fast length (hours) 16) on the example date Wednesday, September 30, 2026: A 16-hour fast that starts at 8:00 PM on September 30, 2026 ends on Thursday, October 1, 2026, 12:00 PM.

Method: End = start date and time + fast length (rounded to the nearest minute); for a fast under 24 hours, eating window = 24 − fast length, closing 24 hours after the fast started.

  • Times are clock times on the calendar with no time zone or daylight saving change during the fast.
  • A daily plan such as 16:8 repeats every 24 hours: fast for 16 hours, then eat within 8.
  • This is a timing tool, not medical advice. Ask a health care provider before fasting if you are pregnant, have diabetes, take medicines, or have had an eating disorder.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Fast starts on 2026-09-29, At 20:00, Fast length (hours) 16 gives Your fast ends Wednesday, September 30, 2026, 12:00 PM, End date 2026-09-30, End time 12:00, Eating window 8 hours, Eating window closes Wednesday, September 30, 2026, 8:00 PM, Fast length in minutes 960.Source: Clock arithmetic with 1 h = 60 min and 1 d = 24 h (NIST SP 811): 8:00 PM + 16 hours = 12:00 PM the next day
  2. Fast starts on 2026-12-31, At 18:30, Fast length (hours) 18.5 gives End date 2027-01-01, End time 13:00, Eating window 5 h 30 min, Fast length in minutes 1,110.
  3. Fast starts on 2026-10-05, At 19:00, Fast length (hours) 36 gives Your fast ends Wednesday, October 7, 2026, 7:00 AM, Fast length in minutes 2,160.

How it works

1. Fast length in minutes. minutes = fast length in hours × 60, rounded half up to a whole minute (16.25 hours is 975 minutes). The fast length can be 1 to 168 hours.

2. The end. Add the minutes to the start (the date and time of the last meal): minutes past midnight at the start + fast minutes, carried into whole days (1,440 minutes each) on the calendar. The headline reads like "Wednesday, September 30, 2026, 12:00 PM" (weekday, date, 12-hour time). The end date and the end time (24-hour, HH:MM) are also given on their own.

3. Daily plans. When the fast is under 24 hours (1,440 minutes):

  • eating window = 1,440 − fast minutes, shown as whole hours ("8 hours", "1 hour") or as hours and minutes ("5 h 30 min");
  • the eating window closes 24 hours after the fast started, written like the end.

For a fast of 24 hours or more there is no daily eating window, and those rows are left out.

Rounding. Every “rounded half up” on this page reads the decimal value: a result within 1e-9 (relative) of a half counts as the half. For example, 80 ÷ 1.6², which a computer stores as 31.249999999999993, rounds to 31.3.

Assumptions

  • Times are clock times with no time zone change and no daylight saving change during the fast.
  • A daily plan repeats every 24 hours.
  • This is a timing tool, not medical advice. Ask a health care provider before fasting if you are pregnant or breastfeeding, have diabetes, take medicines, or have had an eating disorder.

Worked examples by hand

16:8 from 8:00 PM on Tuesday, September 29, 2026. 16 hours = 960 minutes. 8:00 PM is 1,200 minutes past midnight; 1,200 + 960 = 2,160 = 1 day + 720 minutes, so the fast ends on Wednesday, September 30, 2026, 12:00 PM. Eating window: 1,440 − 960 = 480 minutes, 8 hours, closing on Wednesday, September 30, 2026, 8:00 PM.

18.5 hours from 6:30 PM on December 31, 2026. 18.5 × 60 = 1,110 minutes. 6:30 PM is 1,110 minutes past midnight; 1,110 + 1,110 = 2,220 = 1 day + 780 minutes, so the fast ends on January 1, 2027 at 13:00 (1:00 PM). Eating window: 1,440 − 1,110 = 330 minutes, 5 h 30 min.

36 hours from 7:00 PM on Monday, October 5, 2026. 2,160 minutes; 1,140 + 2,160 = 3,300 = 2 days + 420 minutes: Wednesday, October 7, 2026, 7:00 AM. No daily eating window.

Other questions people ask

How do I work out when my fast ends?

Add the fast length to the time of your last meal. A 16-hour fast that starts at 8:00 PM ends at 12:00 PM the next day. The calculator carries the hours over midnight and across months and years for you.

What does 16:8 mean?

Fasting for 16 hours and eating within the other 8 hours of each day. 18:6 is an 18-hour fast with a 6-hour eating window, and 20:4 a 20-hour fast with a 4-hour window. The two numbers always add up to 24.

When does my eating window close?

For a daily plan, the eating window closes 24 hours after your fast started, when the next fast begins. With a fast from 8:00 PM to 12:00 PM, you eat between 12:00 PM and 8:00 PM, then start again.

Can I enter a fast longer than a day?

Yes, up to 168 hours (7 days). The calculator shows when it ends. There is no daily eating window for fasts of 24 hours or more.

Can I use half hours?

Yes. Enter 16.5 for 16 hours 30 minutes. The end time is rounded to the nearest minute.

Is intermittent fasting safe for everyone?

No. People who are pregnant or breastfeeding, have diabetes or take medicines that affect blood sugar, or have had an eating disorder should talk to a health care provider before fasting. This page only does the clock arithmetic.