Default on 401k due to work related disabilty

Dropped working may10 2017;  had $18000 401k loan;  defaulted this year; no earned income at all this year just WC;  how much taxes will I pay on defaulted loan?

Depends on your age.  You are taxed at marginal rates regardless but if you are under the min. distribution age, you pay an additional 10% penalty

one more comment - if you are "totally and permanently" disabled, even if under 59 1/2 you may not have to pay the additional 10% penalty.  You should check with your tax advisor.