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How is the wasabi wallet fee is calculated? I heard the minimum amount of fee is $0.003% which will be will be multiplied by the total number of participants. But the total number of participants is 100. Which means the fee will be 0.3%? Also I learned the fee can be edited and customized, is that true?
Indeed, 0.003 per anonimity set, so yes, in your example that would be a 0.3% fee.
This fee is not customizable.
However, there are some additional rules that do influence the fee, like for example: the smallest participant doesn't pay a fee, remixing is cheaper, tx fee fluctuations have an impact, very small change can get added to the fee.
This makes it very hard (if not impossible) to say which fee you'll pay beforehand... But overall, i've never overpayed compared to traditional mixers (chipmixer is an exception since it allows you to chose your own fee), but most mixers charge >1% as a mixing fee, and so far i've never payed more than 1% using wasabi's coinjoin implementation.