Ideally, if you’re seeking a healthy sum in retirement, you’ll invest the maximum amount in the IRA annually. If you’re under age 50, that’s $541.66 per month, which equates to $6,500 per year. Those over age 50 can invest $625 per month, which is equal to $7500 per year. If you can’t swing the maximum, then invest as much as you can afford. You can always increase your IRA contributions later.