Hi, Can Keypay calculate the tax witheld and superannuation backwards from the Net pay of wages?

Hi ivana1, 

The payroll system works to calculate net and tax based off the gross earnings, not the other way around. If you wish, you can review the gross pay estimator calculator provided by the ATO by clicking here. This would be the best work around for the time being as the current payroll software is set in this method of calculation. 

Thanks, 

Steven