I give maximum amount to my employer 401k plan and would like to also put some in an after tax (ROTH) IRA. How much can I put in an IRA? Is there a limit? I'm 51 - I think that might matter.

What also matters is what you earned (your annual salary) to determine whether you can contribute to a Roth IRA.

Since you are over 50 the maximum contribution you can make to all traditional and Roth IRAs is $6000 per year (if you were under 50 the limit is $5000). You may contribute this maximum to a Roth IRA if your adjusted gross income for 2013 is less than $178K if married filing jointly or less than $112K if single. If your income exceeds this then you may be able to contribute a reduced amount, or perhaps none at all to a Roth and could instead fund a traditional IRA - post back if you want more detail on the income limits. If you exceed the income limit for contributing to a Roth IRA one strategy to consider is to contribute to a traditional IRA and then convert it to a Roth. There are no income restrictions on contributing to a traditional IRA, but depending on your income level the contribution may not be tax deductible.