We forgot to declare a small stock sale and long term capital gain on our 2014 taxes so just received a CP2000 and proposed amount due in additional taxes. Which I hear is very common.

I understand that the IRS does not have information regarding the cost basis so this proposed amount is higher than the actual amount we owe...but my questions are:

- How do I best determine how much we actually owe?
- Do I have to determine that when I send them the response or just send them the associated 1099-B with a letter and wait for them to tell me how much I actually owe?
- Do I have to fill out the entire Schedule D and 8949 (worksheet is very complicated and difficult to navigate)?
- Do I need to file an amended tax return to achieve this even though it explicitly says I don't on the CP2000?

Here is some general (rounded) information.

1099-B
Acquired 1/2010 Sold 3/2014
Proceeds $7,000
Cost Basis $5000
Gain $2000

Corrected taxable income (including this gain) $365,000

My tax program says I owe $500 when I plug all this into an amended return...is that possible for such a small gain?! I though long term capital gains were taxed at 20% maximum or closer to $400...

Thanks!