Good calculator recommendations?

I am about 4 years away from planned retirement (I am 56) and somewhat freaked out that I have saved too much in my 401K for tax purposes in the future. I did start last year converting portions to Roth 401K, when my employer added that option. I have a very small taxable brokerage account on the side but my primary focus in the next few years is converting to Roth 401K as much a possible. I will file for Social Security at 62. I do plan to eventually meet with a CPA for more specific guidance, but can anyone recommend a good free website where I can put these planned numbers in and understand them in relation to my tax brackets? Also, I would appreciate any recommendations of good videos about this (tax planning for those with most money in their 401K. I am head of household, so won't have as much bracket as married couples.