Will taxes in retirement be lower?

There are two views on how taxes will change in retirement. Some say they will go up or stay the same, the others say they will go down. Who is right? 

I wanted to know the answer when I got a recommendation from my 401k administrator to convert my 401k to a Roth 401k. 
He is convinced that it will be beneficial for me to convert and pay taxes now and get the distributions tax free later when I am retired. Yes I am in a high tax bracket now. But will it really stay the same in retirement? 


One possibility is that taxes in retirement will be the same or increase. This notion is mainly based on the fear and the experience that lately the taxes are more often increasing and rarely decreasing. 

The second view is that the taxes in retirement will be lower. This view is based on current tax code and the expectation that the tax laws will not change very much. 


When you work, you mostly just get a salary as a source of income - as one type of income.
When you retire, you will have different types of income. And the tax rules are different for different types of income. 

Here is the list of the most common types of income in retirement: 

1. Social Security benefits
This will only be taxed if you have additional income. No other income - no tax.
If you have additional income, up to 85% of Social Security benefits can be taxable.

  
2. 401k distributions
Traditional (non-Roth) 401k - the withdrawals will be taxed.
Roth 401 - withdrawals are not taxed.


3. IRA distributions 
Traditional IRA - withdrawals will be taxed. 
Roth IRA  - withdrawals are not taxed.


4. Investment gains (from taxable accounts)
Taxed will be dividends, capital gains (short or long term) and interest. 
If you are a HIP (=high income professional), you will "run out space" in your 401k and IRA due to the contribution limits and will have taxable savings and investment accounts with dividends, interest and capital gains.



5. Annuities
Some will have annuity distributions. Depending on the type of annuity different tax rules will apply.



I used various calculators, they are complicated. At the end I have an impression that my taxes in the retirement will either stay the same or will be lower. I asked my CPA and she hedged with "It is not possible to predict but generally the taxes are lower in retirement". 

I used various calculators, some were simple, some complicated. At the end I have an impression that my taxes in retirement will either stay the same or will be lower. 
That may influence some decisions like 401k to Roth 401k conversion. 
But overall it would be best just to have so much money that taxes will not matter.