See earlier question:<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/2895811-paying-taxes-on-403k-loan-i-was-just-told-that-i-may-choose-to-pay-the-30-000-loan-from-my-403k-as-added-income-rather-than-continue-to-make-a-quarterly-2-000-payment">https://ttlc.intuit.com/questions/2895811-paying-taxes-on-403k-loan-i-was-just-told-that-i-may-choose-to-pay-the-30-000-loan-from-my-403k-as-added-income-rather-than-continue-to-make-a-quarterly-2-000-payment</a>
It depends upon your overall tax situation, but plan on at least 30-40% for Federal + State + 10% penalty. See this Federal estimating tool:
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/