A little more clarification: I don't know of any MLP websites that have a calculator. However, as Edijac point out, several of the K1 sites at www.k1support.com
have a calculator that allows you to calculate how much Ordinary Income and Cap Gain would result IF you sold your holdings on 12/31/2010. Since we're almost two distributions past that point, those numbers have changed but its probably the best estimate you'll get. Note it only works if you owned the MLP in 2010 and have a K1 at the website.
As an example - here's something I posted on Yahoo a few weeks ago using the calculator:
"As a quick example, I bought EPD early in 2006. If I had sold on 12/31/2010, according to their calcs (I've normalized all numbers to 100 shares similar to the UBTI project) I would have Ordinary Income of approx $1500/100 shares and Cap Gain of approx $2000 per 100 shares. However I also have carryforward losses of approx $725 per 100 shares which will windup on Sched E and in effect "offset" almost half of the ordinary gain. Also had distributions of about $1000/per 100 shares, which if you do the math means upon sale, about 75% of those were taxed as Ordinary Income (after the Sched E offset) , the balance being taxed as Cap Gain "
Note the calculator does not tell you your carryforward losses or distributions. That info is in Turbo Tax or is readily available by looking at the old K1 forms.
As far as what I actually wound up with in my pocket? If I sold, I would have netted approximatel $1900 (per 100 shares) on the sale (proceeds - purchase price) and approx $1000 in distributions. I'm ignoring some very minor texes paid on Portfolio income (interest, etc) passed through