Why are withdrawals the same every year?
In every scenario I have tried, my retirement account withdrawals are the same amount every year (from the year I specified as the year for the first withdrawal). Similarly, my wife's withdrawal amount is the same in every year. I would expect the amounts to vary in different years. For example, I would expect that as regular assets are drawn down and therefore throw off less earnings, the amount withdrawn from retirement accounts would rise (to make up the difference and also because more of the retirement withdrawal would be taxed at lower rates). Also, I would think that the amount withdrawn from retirement accounts would change when I or my wife starts receiving Social Security. I would also expect that the amount withdrawn would change when a person's regular IRAs are depleted and withdrawals start to be taken from Roth IRAs. In this last case, I see a change in taxes paid when the switch from regular to Roth happens, but the amount withdrawn stays the same.
Can someone explain why a given person's retirement withdrawals are the same for every year? Or is it just an assumption of the program that you would want to withdraw the same amount every year. (I understand that you ARE forced to withdraw a constant amount every year if you start before age 59.5, but it is my understanding that constant withdrawals aren't required otherwise, and it seems to me that an optimal strategy would call for different withdrawal amounts in different years.)