In this segment of "Financial Planning Q&A" on Motley Fool Live, recorded on Dec. 1, retirement expert Robert Brokamp outlines the formula to use when estimating retirement expenses.

Robert Brokamp: Two more minutes left here. Let's see if we can get a few questions. Neil says, "Can you buy stocks on leverage in a Roth IRA account?"

There's more to his question but I'm just going to answer it, and the answer is generally, no. You cannot use margin in IRAs. There are some investments that have margins built into them like these leveraged ETFs.

Depending on your IRA provider, you can use some options strategies, but they're limited. But generally, no, you cannot use leverage within an IRA and you cannot borrow against an IRA, unlike a 401(k) -- if your plan allows it.

Then, Mark, the train operator, says: "I'm finding many websites that estimate retirement income. Can you direct me to a website that estimates retirement expenses? I want to make sure that I'm not missing anything."

Yes, Mark, I put this in Slido. It's at the very bottom at this point. It's the Vanguard retirement expenses worksheet, so that's one. You can just Google for other ones. I would say really what it comes down to is listing out all your expenses that you have today, subtracting any that will go away once you retire, and then add in any that will be part of your retirement budget like vacations.

The big one really, though, is healthcare. Because you're probably retiring from a business that provides health insurance and then after you retire, you're on your own. That's really the big expense that will change once you retire. But again, the Vanguard retirement expenses worksheet, I put it in Slido or you can just Google it.