I found the answer here. It's a variable tax rate based on salary in Afgahani, not dollars.
| Gross Income | tax rate |
| 0-60,000 | 0% |
| 60,000-150,000 | 2% |
|150,000-1,200,000| 10% + AFN1800 |
| 1,200,000 | 20% + AFN106,800 |
Can you file it online? : No
Mark Johnson's answer is essentially correct. The income you're speaking of is not likely to be interest income, but the same principle applies: you can file an amended return.
To answer the questions posed in the body of the text:
Should I have mentioned that I own stock in the company I work for?
Since the tax is an income tax, you do not need to ...
I have never had to deal with US Taxes.
For me, listening to such stories and general reading about this topic is like watching a vampire horror movie on television - knowing that they will never get out of the screen.
I do remember statements being made that corrections to an existing tax return can be made.
The advice generaly given was ...