Body fat estimates can change because circumference measurements are sensitive to small differences in tape placement, posture, hydration, bloating and how tightly the tape is pulled. A 1–2 cm difference in waist, neck or hip measurement can noticeably change the final result. Focus on long-term trends rather than one single reading.

Measuring once every 2 to 4 weeks is usually enough. Daily or weekly measurements can fluctuate too much due to water retention, digestion, stress, training soreness and hormonal changes. For the most reliable trend, measure at the same time of day and under the same conditions.

If you are very muscular, the calculator may not perfectly reflect your true body composition. Circumference-based formulas can sometimes overestimate or underestimate body fat in athletes, bodybuilders or individuals with unusually high muscle mass. Use the result as a tracking tool rather than an absolute measurement.