Guides and explainers
Plain-English breakdowns of the numbers behind the calculators, with sources you can check.
BMI vs Body Fat Percentage: When Each One Misleads You
BMI is quick but blind to muscle, while body fat percentage is richer but harder to measure. Here is how each one works and when to trust it.
ReadBMR vs TDEE: What Each Number Means and How They Relate
BMR is the energy you burn at complete rest, while TDEE is your full daily burn including movement and digestion. Here is how they fit together.
ReadHow to set a calorie deficit to lose fat
Fat loss rests on one simple idea: spend more than you eat. Here is how to set your deficit without starving.
ReadCalories Burned Walking, Explained
Walking burns calories in proportion to your body weight, your pace and how long you keep moving. Here is how to estimate it without guessing.
ReadCalories In vs Calories Out: Energy Balance Explained
Energy balance is the simple rule behind weight change: calories in versus calories out. Here is what it really means and where it gets nuanced.
ReadHow accurate is BMI, really
BMI is everywhere, but it has clear limits. Here is what it is good for and when you need other numbers.
ReadHow Many Calories to Build Muscle
Muscle needs a small calorie surplus on top of maintenance. Here is how big to make it and how to grow with minimal fat gain.
ReadHow Many Calories to Maintain Your Weight
Maintenance calories are the amount that keeps your weight steady. Here is how to estimate the number and confirm it in real life.
ReadHow Much Protein Per Day to Lose Weight
Protein is the most important macro when you are losing weight. Here is a practical daily target that protects muscle and curbs hunger.
ReadHow much protein do you need to build muscle
Protein targets get argued to death online. The research is actually pretty settled. Here is the range that builds muscle and how to reach it.
ReadHow Much Water Should You Drink a Day
There is no single magic number for water. Your needs shift with heat, exercise, and body size. Here is how to find a target that fits you.
ReadHow to Calculate Lean Body Mass: Formulas and Why It Matters
Lean body mass is everything in your body that is not fat. Here is how to estimate it with the Boer formula and why the number is worth tracking.
ReadHow to Calculate Macros for Cutting
Cutting is not just eating less. It is eating in a deficit while keeping protein high enough to protect muscle. Here is how to set your macros.
ReadHow to Calculate Max Heart Rate
Max heart rate helps you set training zones. Here are the common formulas, their limits, and how to turn the number into zones.
ReadHow to calculate your TDEE (and actually use it)
Your TDEE is the number every diet math starts from. Here is how to work it out and turn it into a calorie target you can hit.
ReadHow to Estimate Your One Rep Max
You can estimate a one rep max from a set you already did. Here are the Epley and Brzycki formulas and how to use them safely.
ReadHow to Reverse Diet Safely After a Cut
After a cut, jumping back to old habits often backfires. A reverse diet raises calories in small steps so you keep results and feel human again.
ReadHow to Set a Daily Step Goal
A step goal only helps if it fits your life. Here is how to set a realistic target and grow it without burning out.
ReadHow to set your macros for your goal
Macros sound technical but the order is simple. Set protein, set fat, let carbs fill the rest. Here is how to do it from your calorie target.
ReadIdeal Body Weight Formulas: Devine, Hamwi, and What They Really Tell You
Ideal body weight formulas give a quick target number from your height, but they were built for a narrow purpose. Here is how they work and where they fall short.
ReadResting Metabolic Rate Explained
Most of the calories you burn happen while you do nothing. Resting metabolic rate is that baseline, and it drives your daily energy needs.
ReadSteps to Calories, Explained
Turning step counts into calories is possible, but it depends on stride, weight and pace. Here is how the conversion really works.
ReadWaist to Height Ratio Explained: Why 0.5 Is the Number to Watch
Waist to height ratio is one of the simplest health checks you can do at home. Here is how it works, the 0.5 threshold, and why it often beats BMI.
ReadWhat is a healthy body fat percentage
Body fat percentage says more than the scale. Here are the healthy ranges and how to measure them without pricey gear.
ReadWhat is a one-rep max (1RM) and how to estimate it
1RM sits at the heart of any strength program. Here is how to estimate it safely and use the percentages in your training.
ReadFrequently asked questions
The CalcFitLab blog is where the calculators get explained in plain English — what each number means, where the formula comes from, and how to act on the result. Every guide cites its sources and links back to the tool it covers. Here are the questions readers ask most.
What do the CalcFitLab guides cover?
The guides explain the numbers behind the calculators: how TDEE is worked out, why protein targets land where they do, what BMI does and does not tell you, and how to read a one-rep-max estimate. Each one is written to stand on its own and links back to the tool it explains.
Who writes these articles?
They are written by the CalcFitLab editorial team — coaches and reviewers who work with the Trainera platform. Every health claim is tied to a named source such as the NHS, WHO or ACSM, so you can check it rather than take it on trust.
How often are the guides updated?
Each article carries a published and an updated date. When a guideline changes or a better source appears, we revise the piece and re-date it instead of leaving old numbers in place.
Do I need to read a guide to use a calculator?
No. The calculators work on their own. The guides are there for when you want to understand where a number comes from or how to act on it, not as a step you have to take first.
Are the guides free?
Yes. Everything on CalcFitLab is free and needs no sign-up. There is no paywall and no account — you can read any guide and use any tool as often as you like.
Which guide should I read first?
If you are setting up a plan, start with the TDEE and macro explainers, because those numbers drive everything else. From there the training and body-composition guides add detail.