Overview
Starting a ketogenic or low-carb diet without a plan usually means guessing at portion sizes and hoping for the best — and guessing is exactly what causes most people to either stay out of ketosis without realising it, or under-eat protein and lose muscle instead of fat. This guide walks through the actual numbers: how many net carbs you can eat, what your fat and protein targets should be, and how fiber fits into the picture, using free calculators at each step so you're working from your own data instead of a generic meal plan.
Whether you're starting keto for weight loss, blood sugar management, or another reason, the sequence below — set your calories, set your macros, track your net carbs, hit your fiber target — applies the same way. This isn't medical advice; if you have an existing health condition, talk to a doctor before making major dietary changes.
Step 1: Calculate Your Daily Calorie Target
Before setting any macro ratio, you need a calorie baseline. Use the TDEE Calculator to estimate your Total Daily Energy Expenditure — the number of calories your body burns in a typical day accounting for your activity level. If your goal is weight loss, you'll eat below this number; if it's maintenance or muscle preservation while in ketosis, you'll eat close to it.
Getting this number right matters more than most people expect. Too aggressive a deficit on keto can make the diet harder to sustain and increase the risk of losing muscle along with fat, while too small a deficit means slower progress than you might expect.
Step 2: Set Your Keto Macro Ratios
With a calorie target in hand, use the Keto Calculator to convert that number into grams of fat, protein, and carbs. A standard ketogenic split allocates roughly 70–75% of calories to fat, 20–25% to protein, and only 5–10% to carbs — but the calculator converts these percentages into actual gram targets based on your specific calorie number, since fat has 9 calories per gram while protein and carbs have 4.
If you'd rather have more flexibility in which foods you eat, without a fixed keto-style ratio, the IIFYM Calculator sets macro targets using the same underlying logic but without forcing the strict keto fat percentage — useful if you're doing a more general low-carb approach rather than committing to full ketosis.
Step 3: Track Net Carbs, Not Total Carbs
This is the step most beginners get wrong. Nutrition labels list total carbohydrates, but what actually matters for ketosis is net carbs — total carbs minus fiber, since fiber isn't digested the way sugars and starches are. A food that looks high-carb on the label (like a high-fiber vegetable) might have almost no impact on your net carb count.
Use the Net Carbs Calculator to subtract fiber from any food's total carb count before logging it against your daily limit, and the Carb Calculator if you want a broader daily carbohydrate target for a less strict low-carb approach. Consistently checking foods against these two tools is the single biggest factor in staying in ketosis reliably.
Step 4: Don't Skip Your Fiber Target
Because keto and low-carb diets restrict carbs so heavily, it's easy to accidentally under-eat fiber — many high-fiber foods (whole grains, legumes, some fruits) are also higher in net carbs. Use the Fiber Calculator to set a target based on your age, sex, and calorie intake, then prioritise low-carb, high-fiber foods like leafy greens, avocado, chia seeds, and nuts to hit it without blowing your carb budget.
Adequate fiber intake supports digestion and can help offset some of the digestive adjustment period ("keto flu") that many people experience in the first week or two.
Step 5: Recalculate as Your Weight Changes
Your calorie and macro targets aren't fixed — as you lose weight, your TDEE drops, and a calorie target that created a deficit at your starting weight can become a maintenance level a few months in. Revisit the TDEE Calculator every few weeks (or whenever progress stalls) and regenerate your keto macros from the updated number using the Keto Calculator.
This recalculation step is also the moment to adjust for changes in activity level — if you've started exercising more since you began, your protein and calorie needs will be higher than when you first set your targets.
Key Terms
- Macronutrients — the three nutrient categories (fat, protein, carbohydrate) that provide calories and make up your daily macro targets
- TDEE — Total Daily Energy Expenditure; the total calories your body burns in a day including activity
- Net Carbs — total carbohydrate grams minus fiber grams, the figure that matters most for staying in ketosis
- Ketosis — a metabolic state where your body burns fat for fuel instead of glucose, typically reached by keeping net carbs very low
- IIFYM — "If It Fits Your Macros," a flexible dieting approach built around hitting gram targets rather than following a fixed food list
For a fuller definition, see our glossary entry on Keto.