Is there any way to model my taxes for 2021 tax year, if I change my retirement contributions from traditional 401k to Roth401

[abcheers]

I understand that I will be investing with Post tax instead of Pre tax, however, I would like to know if that will change my tax bracket

[MinhT1]

It depends on your current tax bracket and the amount you are contributing to the 401(k).

Please see the tax brackets in this TurboTax article.

Find the tax bracket corresponding to your current taxable income. Add the amount you plan to contribute to the 401(k) to your taxable income to see it you are pushed to the next bracket.