How is RMD (Required Minimum Distribution) withdrawn, say the 4% RMD is withdrawn from each account separately (IRA, 403B, SEP IRA, Simple IRA) or is it computed on the entire retirement accounts and you can withdraw the total from any account(s) you desire?
For IRAs (including SEP and SIMPLE IRAs), RMDs are calculated for each of your IRAs, and you can choose whether to aggregate and withdraw it all from one account or split it. As long as at least the total RMD amount comes out of your IRAs, it doesn't matter which one it comes from.
403(b) accounts are similar to IRAs. RMDs are calculated for each account but the aggregate amount can be taken from one or more accounts.
RMDs for 401(k) and 457(b) plans must be calculated and withdrawn from each plan - if you have multiple 401(k)s, you can't pull the total RMD from just one.
RMDs for one type of account can't be pulled from another type of account. So if you have an IRA and a 403(b), you must take an RMD from each.