Show Stock Quantity Remaining as Percentage %

Hi,

I am just looking into setting up a shop for a client selling shares in an entity and we need to be able to show how many shares (stock quantity) are left as a percentage in the same way this site works https://www.middlehamparkracing.net/horses.htm. Does anyone know how I can do this as have looked for a plugin but can’t find one?

Regards,

Jim Isles