You can go back three years from the original deadline of the tax return to get a full refund. After three years, you will not be able to obtain a refund. It is important if changes are needed on an already filed return that these changes are made within the three year time frame.
http://www.standard.net/Tax-Talk/2014/12/16/How-far-back-can-a-tax-refund-go
The good news is that the IRS does not require you to go back 20 years, or even 10 years, on your unfiled tax returns. In most cases, the IRS requires you to go back and file your last six years of tax returns to get in their good graces. And then, to make arrangements on payment of what is owed. That’s right, a fairly reasonable and more manageable six years and working with IRS collections on payment options.
http://howardlevyirslawyer.com/2015/01/04/how-far-back-should-i-go-on-my-unfiled-tax-returns/
The six year enforcement period for delinquent returns is found in IRS Policy Statement 5-133 and Internal Revenue Manual 1.2.14.1.18. Part of the reason the IRS requires six years is manpower – the IRS cannot administer and staff the enforcement of unfiled tax returns going back as far as 10 or 20 years. And believe it or not, the IRS’s records rarely, if ever, go back that far.
http://howardlevyirslawyer.com/2015/01/04/how-far-back-should-i-go-on-my-unfiled-tax-returns/
Most unclaimed tax refunds belong to people who did not make much money during the year, and therefore are not required to file a tax return. That’s right, the IRS actually tells you that if you make below a certain amount each year, you don’t have to file a return.
http://blog.turbotax.intuit.com/tax-refunds/unclaimed-tax-refunds-what-they-are-and-how-to-get-them-back-12/
If you were owed a refund on any of those prior year tax returns, you can only collect it if you file the return within three years of the original tax deadline. Keep in mind that the IRS will expect you to pay any amount you owe.
http://thelawdictionary.org/article/how-far-back-can-you-file-taxes/
Filing back taxes can be tricky because you'll need to have appropriate forms and instructions for the missing year or years. You'll need your W-2 and any 1099 forms from that year. You may obtain them by contacting your employer. If this isn't possible, you can download Form 4852 from the IRS website.
http://thelawdictionary.org/article/how-far-back-can-you-file-taxes/
First, in order to collect a refund, a tax return must be filed with the IRS no later than three years from the due date of the return. After that, the money gets absorbed by the treasury, so you should stay on top of it. There is no penalty for filing a late return if you qualify for a refund.
http://blog.turbotax.intuit.com/tax-refunds/unclaimed-tax-refunds-what-they-are-and-how-to-get-them-back-12/
How Far Back Can You File a Tax Return? The IRS requires that you file a tax return for every year that you are eligible. Accordingly, you can file as far back in time as you'd like. So if you were required to file a tax return in 1994, but just didn't realize you were supposed to, it's still not too late to fix it. However, the IRS is most concerned with tax records over the last seven years.
http://thelawdictionary.org/article/how-far-back-can-you-file-taxes/
In addition, if you haven’t filed your taxes from previous years, you must do so within the three years in order to get a refund. Past year returns must also be filed in paper form directly to the IRS. It takes 10 to 12 weeks to process an amended tax return and it could take longer to process past year returns.
http://www.standard.net/Tax-Talk/2014/12/16/How-far-back-can-a-tax-refund-go
On the IRS’s end, they can go back three years to adjust returns. If a return is pulled for an audit and something within that return needs to be corrected, the IRS can pull returns farther back to audit. If you owe the IRS they can collect for 10 years for any tax liability. Overall, it is important to file amended and past year returns in a timely manner, especially if the IRS owes you a refund. Tracy Bunner is an enrolled agent and tax preparer with an office in Harrisville.
http://www.standard.net/Tax-Talk/2014/12/16/How-far-back-can-a-tax-refund-go
how many years can i file back taxes
I can file  six years back taxes. You can file back taxes after six years. You can file back taxes for six years.