What to Check Before You Trust an Online Calculator
A short checklist for deciding whether an online calculation is suitable for a quick estimate or needs to be verified elsewhere.
In this guide
Understand what the result represents
Before using a number, make sure you know what was calculated. A percentage increase, a percentage-point change and a percentage of a total are different questions even though the words can sound similar.
Check the inputs
Many wrong answers are really input mistakes. Check units, decimal places, dates and which value is treated as the original or reference value.
Try a simple example
If you are unsure whether a calculator is behaving correctly, test it with numbers whose answer you can work out yourself. A simple 100-to-120 example is often enough to spot a misunderstanding in a percentage calculation.
Verify important decisions
A calculator is useful for arithmetic, but it does not know every rule or circumstance around your situation. If the result affects tax, contracts, regulated requirements or a significant financial decision, verify the underlying rule and assumptions with the appropriate source.
Try the related tool
If you came here because you need to do the calculation or create something now, you can use the matching KingToolsKit tool and then come back to the guide when you want the explanation.
Open the tool →