This document contains general information on taxes, and is not tax advice. Tax laws change, and the information here may not apply to your specific tax situation. Proceed at your own risk.
The IRS has lots of information for what income is taxable. You should start there.
The Graduate Assembly has also prepared a PowerPoint presentation on how to file your taxes as a grad student.
ASUC provides a tax clinic through the Student Legal Clinic for members of the Berkeley community. International students may want to check out tax workshops offered by Services for International Students and Scholars. There is also software designed especially for international scholars.
Tax Slides from Carina Cheng's “How to File Taxes” talk (April, 2016)
If you're on a fellowship, watch out for taxes! Unlike payroll, fellowships have no withholding. This means that the money stays untaxed until April 15, when you suddenly have to pay up. If your bill is over $1000 (and it probably will be) for 2 consecutive years, you'll have to pay a penalty. Now, if that money has been sitting in an ING account it's no big deal, because the penalty will be about the size of the interest you made on it, but it is a hassle. To avoid this hassle, you need to increase your withholding on your teaching money. To do this, you used to need to fill out a W4 (available from the staff), but as of Spring 2013, everything is handled online through https://atyourserviceonline.ucop.edu/ayso/. Login there, navigate to “Tax Withholdings”, and increase your monthly withholding so that you'll owe no taxes next April. If you aim too high, you'll get a refund.
If, for whatever reason, you don't get any payroll funds, you can't increase your withholding because there's nothing to withhold, so you'll have to file taxes quarterly to avoid the penalty. Here's how:
The most common confusing part about our situation is how much we need to report to the IRS. Regardless of whether you're on a fellowship, you need to report money reported on a “1098-T” form, which you can get at 1098t.com. The on-line version has more information and breakdowns than the paper version you get in the mail.
Part 1 of the 1098-T form lists qualified expenses. These are the amounts of your fellowship or grant money that has gone toward expenses which qualify as tax-free. The idea is that money you got to pay for tuition and campus fees isn't taxable because the government wants to encourage education. Subtract the boxed amount in part 1 from the boxed amount in part 2 (which represents all of the fellowship and grant money you got), and you have the taxable portion of your fellowship money. (Note: some non-official tax advice at workshops on campus suggests that this number is not actually correct. You should not pay taxes on your health insurance, even though it is effectively listed as a fellowship on your 1098-T. Just report the money from scholarships that you actually pocketed.)
You must report this money as part of your “Wages, salaries, tips, etc.” on your 1040 form. You need to let the IRS know where this money came from, so if, for instance, your non W-2 component is $20,000, write “SCH $20,000” on the dotted line before the box on line 7 of Form 1040(A) (line 1 of Form 1040EZ) so the IRS knows it's from “SCHolarships”. This income is generally the amount of your class pass and health insurance (UC maintains a list of fees for this academic year and past years.), plus any fellowship checks you received. (See note in above bullet point regarding health insurance.)
If this number isn't about $600 or $700 per semester (check it against the fee schedule above) plus any UC fellowship money your received (that is, checks from UC not on your W-2), it's probably because the university messed up your form, which seems to happen a lot. In that case, you can either add up what you've received yourself, or use the web version of the 1098-T to try and spot the mistake.
Naturally, you also have to report any money reported to you on W-2s (from teaching, for instance), 1099-INTs (from your savings account), 1099-DIVs (from your mutual funds), 1099-Rs (from taxable events in your retirement accounts) and so on. If you have money in a retirement account, the interest and dividends are accumulating tax-free or tax-deferred, so you won't get forms for that unless you performed a conversion or took money out early. If you've made any contributions to a traditional IRA you can deduct them from your income, but any contributions to a Roth IRA don't even need to be mentioned on your tax form, since you're going to pay tax on that income normally. Any pre-tax contributions from your paycheck, like DCP or a 401(k), will be handled for you on your W-2, so you don't need to worry about them, either.
If you have any questions about the taxation of money in or moving around retirement funds, try IRS publication 590 (available on the IRS website.)
We usually don't qualify for either of these, because these qualified expenses are paid through fellowships, scholarships, or grants, and not out of our pockets. Here is what the IRS has to say about it.