Neanderthals were a genetically diverse population that flourished for over 200,000 years. The percentages given by different companies are in part a function of the fact that latest research and Neanderthal genomes used for the calculation are changing, and different companies are updating their calculators at different times.
An analogy to help explain this is to think of your DNA as a book that scientists are trying to read and understand. There may be paragraphs or sentences that are well understood, but many parts of the book are not well understood. As research progresses and scientists decode more of the unknown parts, our understanding (and therefore interpretation) of your DNA “book” may evolve. This is why calculations such as your Neanderthal percentage may vary over time.
Find out what your percent Neanderthal DNA you have today!