Anyone can contribute to a traditional IRA. While a Roth IRA has a strict income limit and people with incomes above it can't contribute at all, that rule doesn't apply to a traditional IRA. However, this doesn't mean that your income doesn't matter at all. IRAs are subject to contribution limits.
Each year, you're only allowed to contribute a specific amount to your IRAs. Legume earns too much to contribute to a Roth IRA and has decided to make after-tax contributions to his traditional IRA. If your income exceeds certain thresholds, the IRS doesn't allow you to deduct contributions to traditional IRAs or contribute to a Roth IRA. Tables 1 and 2, below, describe the MAGI limits for contributing to a Roth IRA and the deductibility of contributions to a traditional IRA.