Where you stand

I changed jobs and have an old 401(k)

If that is you, here is what this situation usually involves, in the order it usually comes up: the things worth checking, what each one is, and where the arithmetic for it lives. None of it says what to do.

1. An old plan does not go anywhere on its own, and there is no deadline unless the balance is below the amount the plan is allowed to pay out by itself, which the plan document states.
2. The fees in the old plan's funds, the new plan's funds, and an IRA at a brokerage are three figures that can be put side by side; the fee calculator shows what the difference costs over the years.
3. The backdoor Roth, a way around the Roth income limit explained in the landscape, interacts with any money held in a traditional IRA; where an old balance sits changes that arithmetic.
4. The rule of 55: money left in the plan of an employer you left in or after the year you turned 55 can be reached without the early penalty, and that rule does not follow money into an IRA.
5. Cashing out before 59 and a half means income tax plus a 10 percent penalty, and the account stops growing; a direct rollover moves the balance with no tax withheld. The plan and a CPA each confirm which applies.

Read these

Workplace plans: the 401(k), the 403(b), and the TSP, from the first paycheck to the last
Roth or traditional: two jars, one tax bill
What a one percent fee costs over a working life