Estimate your daily calorie target and build a high-carb / low-carb macro split from your Mifflin-St Jeor BMR, activity level, and goal.
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Quick Facts
Method
Mifflin-St Jeor BMR × activity factor, then a high/low carb split
Protein stays fixed near 1 g per lb of bodyweight; the remaining calories split 65/35 (carb/fat) on high-carb days and 20/80 on low-carb days.
Results
Calculated
Daily Calorie Target
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TDEE adjusted for your goal
High-Carb Day Carbs
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65% of post-protein calories
Low-Carb Day Carbs
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20% of post-protein calories
Daily Protein
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Held constant on both day types
Ready
Enter your stats, then press Calculate to build your carb-cycling targets.
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How Carb Cycling Works
Carb cycling alternates higher-carbohydrate days with lower-carbohydrate days across the week instead of eating the same carbohydrate amount every day. Protein is held constant every day because it drives muscle repair and satiety regardless of the day type. Carbohydrate and fat are the two macros that trade places: high-carb days lean on carbohydrate for fuel and keep fat lower, while low-carb days lean on fat to fill the calories carbohydrate would otherwise provide.
The formula this calculator uses
Enter your sex, age, body weight, height, and activity level and the calculator first estimates your Basal Metabolic Rate (BMR) with the standard Mifflin-St Jeor equation:
BMR is multiplied by an activity factor (1.2 to 1.9) to estimate maintenance calories, or Total Daily Energy Expenditure (TDEE). Your selected Goal then adjusts TDEE by roughly 20% down for fat loss, 0% for maintenance, or 10% up for muscle gain, giving your daily calorie target.
From there, protein is set at about 1 gram per pound of bodyweight on every day — this stays fixed regardless of day type. Whatever calories remain after protein is subtracted are then split between carbohydrate and fat, and that split is what changes: on high-carb days about 65% of the remaining calories go to carbs and 35% to fat; on low-carb days only about 20% go to carbs and 80% to fat. This is a common practical split used by carb-cycling plans — not a single universally fixed number — and you can shift the ratio to suit your own training and appetite once you understand the mechanics.
Interpreting the results
The Daily Calorie Target is your goal-adjusted TDEE and applies on both high- and low-carb days — only the carbohydrate/fat split changes. High-Carb Day Carbs and Low-Carb Day Carbs show the grams of carbohydrate to eat on each day type, and Daily Protein stays the same regardless of which day you're on. A common weekly pattern is 2 high-carb days (often placed around your hardest training) and 5 low-carb days, but the exact ratio is flexible.
These figures are estimates from a population-average formula. Individual metabolism varies, so treat the numbers as a starting point and adjust every 2-3 weeks based on how your weight trend and energy levels actually respond. Consult a registered dietitian or physician before starting a structured diet plan, especially if you have a medical condition.
Frequently Asked Questions
What is carb cycling?
Carb cycling alternates higher-carbohydrate days with lower-carbohydrate days across the week instead of eating the same carb amount daily. Protein is kept constant every day, while carbohydrate and fat grams shift: high-carb days lean on carbs for fuel and lower fat, low-carb days lean on fat to fill the calories carbs would have provided.
How are the calorie and macro targets calculated?
This calculator estimates BMR with the Mifflin-St Jeor equation, multiplies it by an activity factor to get maintenance calories (TDEE), then applies your goal (deficit, maintenance, or surplus). Protein is set near 1 g per pound of bodyweight on every day and stays fixed. The remaining calories are split between carbs and fat: about 65% to carbs and 35% to fat on high-carb days, and about 20% to carbs and 80% to fat on low-carb days.
How many high-carb and low-carb days should I use?
There is no single required split. A common starting pattern for fat loss is 2 high-carb days and 5 low-carb days per week, often placing high-carb days around your hardest training sessions. Adjust the ratio based on training volume, energy levels, and how your weight trend responds over a few weeks.
Is carb cycling better than a flat daily calorie target?
Carb cycling and a flat daily target can produce similar results if total weekly calories and protein match, since body composition change is driven mainly by the weekly energy balance. Carb cycling is a scheduling tool — it times more carbohydrate around training and less around rest days — rather than a different total. Choose whichever structure you can follow consistently.
Practical Guide for Carb Cycling Calculator | Optimize Energy and Fat Loss
Carb Cycling Calculator | Optimize Energy and Fat Loss is most useful when the inputs reflect the situation you are actually planning around, not a best-case estimate. Treat the result as a decision aid: it gives you a structured way to compare assumptions, spot outliers, and decide what to verify next. For Other work, the most important review lens is baseline behavior, time cost, throughput, constraints, friction, and the decision threshold you care about.
Start with a baseline run using values you can defend. Then change one assumption at a time and watch which output moves the most. If one input dominates the result, spend your verification time there first. If several inputs have similar influence, use a conservative scenario and an optimistic scenario to create a practical range instead of relying on a single exact number.
Before acting on the result, compare the result with recent real-world data instead of ideal targets or one-off examples. This is especially important when the calculator supports a purchase, project plan, performance target, or operational decision. The calculator can make the math consistent, but the quality of the conclusion still depends on current data, clear units, and assumptions that match your real constraints.
When the output looks surprising, slow down and inspect each input in order. A small change in one high-leverage field can move the final number more than several low-leverage fields combined. For Carb Cycling Calculator | Optimize Energy and Fat Loss, that means you should first confirm the value with the greatest scale, then confirm the value with the greatest uncertainty, then rerun the calculator with conservative and optimistic assumptions. This sequence turns the calculator from a single answer into a practical decision range.
Review Checklist
Confirm every input uses the unit and time period requested by the calculator.
Run a low, expected, and high scenario so the answer has a useful range.
Check whether rounding or a missing decimal place changes the decision.
Update the calculation after each meaningful workflow, schedule, cost, or usage change.