This investment income is from a gift for a college fund from my great grandfather. I got it as a baby and It matured on my graduation date. Do I owe taxes on the whole?

[rjs]

"This investment income" - What investment income? We can't see your screen or the papers on your desk.

What kind of "fund"? A QTP (529 plan)? An ESA? A UTMA account? A trust? Something else?

What kind of investment income? Interest? Dividends? Capital gains? What type of tax form did you receive that shows the income?

[Opus 17]

The general principle is that you owe tax on the difference between the cost basis and the selling price.

For a straightforward gift, not in any kind of special account, your cost basis is the price that the original giver paid, so you would owe tax on the difference between the sales proceeds and the purchase price.  For a stock or mutual fund, you can look up the original price on line.

However, there are many variations on this, and there are exceptions for certain tax-privileged accounts.  So we really need to know more about what kind of investment or asset was sold, what kind of account it was in, and what kind of 1099 forms you got and what they say.