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There's a big gap between theory and reality when it comes to retirement tax planning. You've probably heard about the zero percent capital gains bracket and how powerful it can be as part of a Roth conversion strategy. And in the right situation, it absolutely is. But for a lot of people, especially those who retire early with other income sources, it can't be the only thing you're looking at.

I want to walk you through a real case study that shows how to think about capital gains and Roth conversions together, while accounting for the income that many retirees actually have, like pension income or rental income. And I want to take it one step further and show you what this actually means for your cash flow, because that part tends to get skipped over in most of these conversations.

The Setup: Four Scenarios, One Couple

Let's take a married couple, filing jointly, both around age sixty. They're retiring early, they have a taxable brokerage account, rental properties generating income, and they're worried about their tax-deferred accounts and future required minimum distributions (RMDs).

For context, if you were born in 1960 or later, your RMD age is seventy-five. So if you retire at sixty, you've got a fifteen-year window to do Roth conversions before the IRS forces distributions on you. That's a long runway, and how you use it matters a lot.

Here are the four scenarios I want to walk through:

1. Capital gains plus Roth conversions (the "do everything" approach)
2. Capital gains, no conversions (let the brokerage account do the work)
3. No brokerage account, just conversions
4. Starting conversions at age sixty-seven, when Social Security kicks in

Let's go through each one.

Scenario 1: Capital Gains Plus Roth Conversions

In this scenario, our couple decides to do a $100,000 Roth conversion every year from age sixty to sixty-seven. They're also living on their brokerage account, pulling out $120,000 per year to cover their lifestyle. Of that $120,000, I'm assuming seventy-five percent is a capital gain, so roughly $90,000 flows through as a taxable long-term capital gain.

On top of that, they have $50,000 in rental income coming in every year. Add it all up and their total income picture is around $240,000. After applying the standard deduction, their total tax bill comes in just under $29,000. Their ordinary marginal bracket is twenty-two percent, meaning the next dollar of regular income gets taxed at that rate. Their capital gains rate on the next dollar is fifteen percent.

Now, fifteen percent on capital gains sounds great on paper. And it is. But it's not the whole story.

Here's what I want you to focus on: the effective rate of the Roth conversion itself. This is a number I think more people should pay attention to. What it's telling you is, what did doing the conversion actually add to your tax bill? In this case, the answer is roughly $25,000. That's the incremental tax cost of converting that $100,000.

So when you look at the full picture, going from a scenario with no conversion to a scenario with a conversion cost this couple $25,000 in additional taxes. That's a real number. And that $29,000 total tax bill? That's coming out of your cash flow in retirement.

Scenario 2: Capital Gains, No Conversions

Now let's look at what happens if this couple just uses their brokerage account and skips the Roth conversion entirely.

Same lifestyle. Same $120,000 from the brokerage. Same $50,000 rental income. The only thing that changes is they're not converting anything.

Their total tax bill drops to just over $3,000.

That's the difference. Going from $28,840 to $3,000 in taxes. The gap between those two numbers is about $25,000, which is almost exactly what I said the conversion was costing them. That's not a coincidence.

Now think about what $25,000 a year means in early retirement. That's more than $2,000 a month that stays in your pocket instead of going to the IRS. What would you do with that in your early sixties? Travel? Home improvements? Helping your kids? For most people, the answer is a lot.

I'm not saying Roth conversions are wrong. I'm saying you need to think carefully about where the money to pay the conversion tax is coming from. It has to come from somewhere. And in a cash flow budget in retirement, that matters in a different way than it did when you were working and earning a salary.

The favorable capital gains treatment is still very much in play here. They're living comfortably, paying very little in taxes, and not touching their tax-deferred accounts at all. For a lot of people in this situation, this is genuinely a very good place to be.

Scenario 3: No Brokerage Account, Just Conversions

This one I'm including mostly to highlight what it looks like when you don't have a taxable brokerage account in retirement. This is an important reason why saving outside of a 401(k) or IRA actually matters.

In this scenario, the couple still wants to live on $120,000 plus the $50,000 rental income, but they have no brokerage to draw from. So that income has to come out of the traditional IRA, and they're also doing the $100,000 Roth conversion on top of that.

Their total tax bill jumps to $43,000. The conversion itself added about $23,000 to that bill. And even though the effective rate of the conversion looks a little lower on paper than scenario one, the dollar amount paid is significantly higher. And their marginal bracket went up.

Effective rates don't always tell the full story. A lower effective rate with a much higher actual tax bill is not a win. This scenario makes the case for why having a taxable brokerage account in retirement gives you real flexibility, both in terms of how you live and how you manage your tax bill.

Scenario 4: Starting Conversions at Age Sixty-Seven

This one might be the most surprising, and it's the one I want to spend the most time on.

Here we assume the couple waited. They spent down their brokerage account from sixty to sixty-seven living on capital gains and rental income, paying very little in taxes the whole time. Now at sixty-seven, Social Security starts. Let's say they're bringing in $60,000 from Social Security, of which about $51,000 is taxable (because eighty-five percent of Social Security benefits are typically included in income at this income level).

Rental income has grown with inflation, so instead of $50,000, let's call it $61,000 after three percent annual increases over seven years. They're still doing the $100,000 Roth conversion. Their total tax bill at sixty-seven comes out to about $37,000.

That sounds worse than the $28,840 in scenario one, right? But here's where you have to think about time value.

That $37,000 is seven years in the future. If you discount it back to the present at three percent, it's worth roughly $30,000 in today's dollars. Compare that to the $28,840 in scenario one and the difference is pretty small. We're talking about a couple thousand dollars of difference on a present value basis.

More importantly, look at the incremental cost of the conversion itself in this scenario. The added tax from doing the conversion is about $22,000. In scenario one, the conversion added $25,000. So you're paying a little less for the same $100,000 conversion when you do it at sixty-seven, and the marginal bracket in both cases is still twenty-two percent. Nothing dramatically changes there.

But here's the big question you should be asking: what did you get in return for waiting?

You got seven years of your early sixties, when you're most likely in your best health, most likely to travel, most likely to spend money on experiences and the things you actually want to do in retirement. You paid very little in taxes during those seven years. And when you finally start the conversions at sixty-seven, you're not paying dramatically more for the privilege of having done that.

What This Actually Means

When I step back and look at all four of these scenarios together, a pattern emerges. For people who retire early and have other income coming in, whether that's a pension, rental income, or something else, blindly doing Roth conversions from day one may not be the best path.

The math often favors living on your taxable brokerage account in early retirement, taking advantage of the favorable capital gains treatment, and keeping your overall tax bill low during those years. Then when Social Security kicks in, you can still do meaningful Roth conversions between sixty-seven and seventy-four, because remember, your RMD age is seventy-five if you were born in 1960 or later. You haven't lost the conversion window. You've just shifted it.

The traditional advice to convert as early as possible makes a lot of sense when you have no income and a large IRA. But when you add rental income, a pension, or other sources into the picture, the analysis changes. You may already be filling up lower brackets with that income, which means your conversion dollars cost more than you think.

And there's the cash flow piece that I don't think gets enough attention. When you're working, paying a big tax bill is painful but manageable. When you're retired and living on a fixed budget, every dollar matters differently. Watching $25,000 leave your account every year for taxes, during your healthiest and most active years in retirement, is a real tradeoff that deserves serious consideration.

A Few Things to Keep in Mind

This is not one-size-fits-all. Everyone's income picture is different, and the right strategy depends on your specific accounts, your specific income, and your specific goals. A few things worth thinking through with your advisor and your tax preparer:

• What income do you actually have coming in during retirement, and how does that affect your brackets?
• How large is your brokerage account relative to your IRA, and how long can it last?
• What is Social Security going to look like for you, and when are you planning to take it?
• What's your actual RMD exposure down the road if you don't convert?

These questions don't have universal answers. But if you skip them and just assume that more Roth conversions are always better, you may end up paying more in taxes during the years when you had the most flexibility to avoid it.

All income is not created equal in retirement. The planning has to reflect that reality.

Forrest Dutton is a Certified Financial Planner and the owner of Brightworks Financial Planning. This blog is for educational purposes only and is not personal financial, tax, or investment advice. Always consult with your financial advisor and tax professional before making decisions.