We know you're busy planning for the upcoming holidays, but December 31 doesn't just mark the end of 2018. It's also the deadline for important tax stuff.

Here are five things you need to do by the end of 2018 to lower your forthcoming tax bill.

1. Maximize your 401(k) contributions.

Money going into an employer-sponsored 401(k) isn't considered taxable income, but you can only subtract funds that hit the account through December 31. If you're looking for a tax break, contact your human resources department to see about making a last-minute contribution. For 2018, you can put up to $18,500 into a employer-sponsored 401(k) plan. That figure jumps to $25,000 if you're 50 or older.

Also, take note: You can contribute more to your 401(k) in 2019.

2. Make a charitable donation.

The IRS lets itemizers deduct charitable donations up to 50 percent of their adjusted gross income, with a few exceptions. You have to make donations by end-of-day December 31 to include them on your 2018 tax return, though.

3. Put more money in a 529 plan.

Contributions into a 529 college savings plan -- a custodial trust fund that helps a beneficiary pay for their higher education -- also don't count as taxable income. As such, this account is another option when it comes to scoring a federal tax break for 2018, as long as you make the contribution by, you guessed it, December 31.

There's no hard and fast limit for how much money you can put in a 529 plan each year. The IRS says contributions can't go over "the amount necessary to provide for the qualified education expenses of the beneficiary."

Still, keep it under $14,000 if you want to avoid gift tax consequences. 

You can read more about tax breaks and regulations in this state-by-state guide to 529 plans.

4. Withdraw your required minimums.

If you're over 70-and-a-half, you actually have to take money out of your retirement accounts, including 401(k)s, traditional IRAs, SEP IRAs and SIMPLE IRAs, each year to avoid a penalty. Those required minimum distributions -- which vary by age and marital status -- must get made by December 31. Otherwise, they'll get taxed at 50 percent. The big exception? If you turned 70-and-a-half in 2018, you have until April 1 to take the distribution.

5. Spend the money in your FSA.

OK, spending the money in your flexible spending account (FSA) -- an employer-sponsored, tax-exempt fund used to save for medical expenses -- won't change much on your 2018 tax return. (The money's deducted from your taxable income when it goes in the account, so you're already getting that benefit.) But funds in those accounts are "use it or lose it," meaning leftover dollars don't necessarily roll over to 2019. Now's the time to see if your employer provides a grace period or allows you to at least roll some funds (up to $500) over to next year. If not, it's time for trip to, say, the dentist, optometrist or drug store. You can put leftover FSA funds toward things like bandages, eyeglasses and breast pumps.

This article originally appeared on Policygenius and was syndicated by MediaFeed.org.