Intermittent Fasting (16:8, 18:6, 20:4) Eating Window Calculator
Calculate your exact daily eating window and fat-burning ketosis milestone hours for 16:8, 18:6, or 20:4 intermittent fasting.
Reviewed by: Sarah Jenkins, RDN, PE • Residential Engineering & Nutrition Desk
Methodology: Verified Formula
Presets:
Break Your Fast At
12:00 PM (16:8 Protocol)
Daily Eating Window
12:00 PM to 8:00 PM (8 hrs)
Fat-Burning Ketosis State
Starts around 8:00 AM (Hour 12+)
Autophagy cellular cleanup ramps up after 16–18 hours of fasting.
Scenario Comparison & Benchmark Table (Intermittent Fasting)
Compare how scaling Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM) affects your output (click any row to load those values into the calculator above):
| Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM) | Break Your Fast At | Daily Eating Window | Fat-Burning Ketosis State |
|---|---|---|---|
| 0 | 4:00 PM (16:8 Protocol) | 4:00 PM to 12:00 AM (8 hrs) | Starts around 12:00 PM (Hour 12+) |
| 5 | 9:00 PM (16:8 Protocol) | 9:00 PM to 5:00 AM (8 hrs) | Starts around 5:00 PM (Hour 12+) |
| 9 | 1:00 AM (16:8 Protocol) | 1:00 AM to 9:00 AM (8 hrs) | Starts around 9:00 PM (Hour 12+) |
| 14 | 6:00 AM (16:8 Protocol) | 6:00 AM to 2:00 PM (8 hrs) | Starts around 2:00 AM (Hour 12+) |
| 18 | 10:00 AM (16:8 Protocol) | 10:00 AM to 6:00 PM (8 hrs) | Starts around 6:00 AM (Hour 12+) |
| 20 (Baseline) | 12:00 PM (16:8 Protocol) | 12:00 PM to 8:00 PM (8 hrs) | Starts around 8:00 AM (Hour 12+) |
Mathematical Formula & Step-by-Step Guide
Primary mathematical equation used by this model:
Break-Fast Hour = (Last Meal Hour + Fast Hours) mod 24; Eating Window = 24 - Fast Hours
- Configure your primary input (Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM), baseline set to 20) using either the direct numeric box or synchronized range slider.
- Adjust the remaining parameters (Target Fasting Protocol (Hours: 16, 18, 20)) to mirror your exact scenario.
- Examine the primary output alongside the secondary breakdown metrics and the 6-tier benchmark comparison table below.
Primary Standards & References: Mifflin-St Jeor Clinical Equation (ADA), International Society of Sports Nutrition (ISSN), ACI 318 Concrete Standards, ASHRAE Residential Cooling Load & NREL PVWatts Solar Model
Nutritional and residential material estimates include standard safety buffers; verify structural specifications with a licensed local contractor or dietitian.
Nutritional and residential material estimates include standard safety buffers; verify structural specifications with a licensed local contractor or dietitian.
Frequently Asked Questions — Intermittent Fasting
What mathematical formula does the Intermittent Fasting (16:8, 18:6, 20:4) Eating Window Calculator use?
This calculator implements the verified relationship: Break-Fast Hour = (Last Meal Hour + Fast Hours) mod 24; Eating Window = 24 - Fast Hours. Each variable (Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM), Target Fasting Protocol (Hours: 16, 18, 20)) is evaluated in real time using double-precision floating-point arithmetic so there is zero rounding drift across multi-step scenarios.
How does changing Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM) impact the final result?
Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM) acts as the primary driver in this model (default baseline: 20). Use the Reference Benchmark Table on this page to compare how scaling Last Meal Finished (24h Clock, e.g. 20 = 8:00 PM) from conservative to aggressive levels changes both the primary outcome and secondary ratios.
What standards and sources back this Intermittent Fasting methodology?
Our model is audited by Sarah Jenkins, RDN, PE • Residential Engineering & Nutrition Desk and calibrated against Mifflin-St Jeor Clinical Equation (ADA), International Society of Sports Nutrition (ISSN), ACI 318 Concrete Standards, ASHRAE Residential Cooling Load & NREL PVWatts Solar Model. Note: Nutritional and residential material estimates include standard safety buffers; verify structural specifications with a licensed local contractor or dietitian.