Featured · Health · 6 min
FFMI — What It Means and How to Calculate It
FFMI is a fat-free mass index used by trainers and bodybuilders. Check the formula, reference ranges for men and women, and a worked example.
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Blog — guides & news
Guides on taxes, salaries, loans and personal finance in Poland — with worked examples and links to ready-made calculators.
Latest articles
Sport · 7 min
Lactate Threshold in Running — What It Is and How to Raise It
Lactate threshold determines how long you can sustain a fast pace while running. Learn how to estimate it, train it, and use it when planning races.
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Health · 7 min
Cutting Diet — How to Set Calories and Macros
A cutting diet is a controlled calorie deficit with adequate protein intake. See how to calculate calories and macros and avoid the most common mistakes.
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Health · 6 min
Vitamin D Supplementation — Dosage and Rules
Vitamin D affects bones, immunity, and muscles. Check recommended doses for adults, when to supplement, and what to look for when choosing a product.
· Redakcja Liczbnik
Health · 6 min
Spine Health for Desk Jobs — How to Take Care of It
Sitting all day strains the spine and weakens postural muscles. Learn how to set up your workstation, which exercises help, and when to take breaks.
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Sport · 7 min
Strength Training for Beginners — How to Build a Plan
Your first strength training plan doesn't need to be complicated. Learn how to choose exercises, sets, and load to safely start building strength.
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Sport · 6 min
How Many Calories You Burn in Yoga and Pilates — Compared
Yoga and Pilates differ in intensity and calorie burn. See how many calories an hour of each class burns and what benefits both forms of training offer.
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Sport · 6 min
Sleep and Athletic Recovery — How to Sleep to Make Progress
Sleep is a key part of post-workout recovery. See how much sleep physically active people need and how a lack of it affects athletic performance.
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Sport · 6 min
HIIT — Is Interval Training Worth It and How to Start
HIIT is high-intensity interval training. See how it works, how many calories it burns, and how to safely start interval training today.
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Health · 7 min
Exercise and Heart Health — How to Train Safely
Physical activity supports cardiovascular health, but it requires a sensible approach. Learn how to choose training intensity and when to get your heart checked.
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Science · 6 min
Coulomb's Law — Formula, Units and Worked Examples
Coulomb's law describes the force between electric charges. Learn the formula, the constant k, and a step-by-step numerical example for 2026.
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Science · 7 min
Entropy — Basics, Formula and Examples in Physics 2026
What is entropy and how do you calculate it? We explain the second law of thermodynamics, Boltzmann's formula, and entropy using simple physical examples for 2026.
· Redakcja Liczbnik
Animals · 6 min
Adopting a Dog from a Shelter — Costs and Formalities 2026
How much does it cost to adopt a dog from a shelter and what formalities are involved? Check the fees, requirements, and the cost of keeping a dog after adoption.
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Calculate the percentage of a number, a percentage increase and a percentage decrease. Free percentage calculator.
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Calculate Polish income tax (PIT) using the 2026 tax scale: 12% and 32%. Includes the PLN 30,000 tax-free amount and the relief for young people.
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Calculate net take-home pay from self-employment (B2B): flat 19% PIT, lump sum or scale. ZUS and health contributions. Free B2B calculator.
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