Savers who put money into traditional IRAs and 401(k)s get a nice tax break. Contributions up to an annual limit exempt some of your earnings from taxes, so if you fund one of these accounts, you get to not only set money aside for retirement, but pay the IRS a little less.

But because your contributions to a traditional IRA or 401(k) plan go in on a pre-tax basis, the IRS wants you to leave your money alone long enough for it to serve as income for retirement. As such, there's a 10% early withdrawal penalty that generally applies to distributions from these accounts taken prior to age 59 1/2.

Now there are a few exceptions. IRAs, for example, allow you to withdraw up to $10,000 to purchase a first-time home. You can also tap an IRA early to pay for higher education.

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But even if you're able to take an IRA or 401(k) withdrawal without incurring a penalty, doing so prior to actual retirement could hurt you in a very big way. Here's why.

It's a matter of lost investment gains

Clearly, a 10% early withdrawal penalty has the potential to cause you financial harm. But even if you're able to avoid that penalty, raiding your IRA or 401(k) might harm you financially in another way.

The money in your IRA or 401(k) shouldn't just sit in cash. Ideally, you're investing that money so your balance grows nicely over time. As such, any dollar you remove from an IRA or 401(k) early is money you can't keep investing. And the consequences there could be huge.

Let's say you take a $10,000 withdrawal from your IRA at age 35 to purchase a home. But let's also assume you then don't retire until age 70. Furthermore, let's assume that your IRA portfolio delivers an average annual return of 8%, which is a bit below the stock market's average.

By missing out on the opportunity to earn 8% on your $10,000 withdrawal over 35 years, you're losing out on almost $148,000 of retirement income. That could potentially constitute a few years' worth of bills for your senior self, depending on what your costs turn out to be.

Be careful even when taking a withdrawal after age 59 1/2

Once you turn 59 1/2, you can remove funds from your IRA or 401(k) without having to worry about a penalty. But even then, it's important to be careful.

Let's say you're thinking of removing $20,000 from your 401(k) to renovate your home at age 60. That money is yours free and clear of penalties. But let's also assume you're not retiring until age 68, and that your portfolio delivers a yearly return of 6% in your 60s (since, by then, it's good to shift to more conservative investments).

Losing out on a 6% return on $20,000 over eight years means missing out on about $32,000 in retirement income. That's still a notable sum. It could, for example, end up being money you need to pay for healthcare down the line.

The fact that the IRS imposes early withdrawal penalties on IRAs and 401(k)s is actually sort of a good thing, since it may be the factor that helps you stay disciplined and avoid tapping your savings prematurely. But even if you're able to avoid a penalty, it still pays to try not to take a withdrawal from your IRA or 401(k) until you're actually retired and absolutely need that money.