Retirement income and taxes

I am moving into full retirement during 2018 and will switch some meaningful income from regular earnings with tax deductions to retirement fund withdrawals. My 2017 TurboTax returns have estimated payment vouchers and seems to indicate so long as I pay at least these values through 2018/19 I will not have any liability for possible underpayments through change of income sources. Is this correct regardless of the income mix change? Thanks.