What is the percentage difference/decrease between 519 (original number) and 4 (new number)?

I have been using an excel formula as well as a calculation website and they both give me a figure of 99%. This does not seem right to me as the difference between the two numbers is so large (much more than 100%). Please can someone explain how this should be calculated - Thanks!
Update: Thanks for your answers however if we would like to explain the percentage change to our client, 99% will not show the clear picture as it can be used to describe any difference that is over a certain amount. In reality the difference between 519 and 4 is - 12875% (using the same formula for if the % change was... show more Thanks for your answers however if we would like to explain the percentage change to our client, 99% will not show the clear picture as it can be used to describe any difference that is over a certain amount.

In reality the difference between 519 and 4 is - 12875% (using the same formula for if the % change was positive and then making it a minus figure).

Is this a viable mathematical way of explaining this to the client?
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