It depends on a lot of variables.

If you want to allow the IRS to have an interest-free loan for a year, you can play it safe, claim ZERO, and you can always adjust it in 2009.

Your other option is to just do a mock tax return. Look at the tax tables, estimate how much you will make, and what you will owe.

2nd job won’t know about earnings from 1st job, and vice versa. They’ll withhold at the level they are paying you at, but the combined income from the two jobs could push you into a higher tax bracket. Probably should claim 0 on 2nd job. Here’s a website that might help overall though, http://www.paycheckcity.com, it’s a paycheck calculator website. You could enter your information from both jobs as if you were having only one job and see what you’d have to have for federal and state withholding and plan accordingly.

If you are making around $5000 on the second job, it’s not going to matter what you put on your W-4 there – they’ll take taxes out as if that was your only job, and since if it was you wouldn’t owe anything, they won’t withhold for federal income tax no matter what you put on your W-4 there. They’ll take social security and medicare, of course, but not income tax. But when you actually do your tax return, the income from the two jobs will add together, and you’ll owe around $750 additional income tax because of the $5000 from the second job.

What you need to do, and I know you aren’t going to want to hear this, is drop your allowances at your FIRST job to zero. They’ll take out around $10 a week extra. That, combined with your refund becoming smaller than it has been, should be enough to cover the extra taxes.

If you keep the first job at 1 and just claim zero on the 2nd job, you’ll probably end up owing $350-$450 when you file your return, instead of getting a refund.