Retirement contributions are a superb way to lower your overall taxable income. Here's how it breaks down: If you have a 401k, you are allowed to contribute amounts up to $18,000. If you're over the age of 50 (or turning 50 this year), you can contribute a total of $24,000 to your 401k. For those with SIMPLE 401k plans, you're capped at $12,500 in contributions, or $15,500 for those 50 or older.