tax on investment profit

What is the name of your state? florida
after buying & rehabing then selling a single family or duplex what is the tax rate on any profit realized on the sale(s);
and is there a roleover available to purchase other properties to avoid paying any taxes on the gain(s)?

Your gain is added to all your other income, and that total minus deductions and exemptions determines your tax rate.

There is nothing I know of which allows you "rollover" the proceeds from one sale to another.

Enjoy the profits, but put enough away to cover the taxes.

[abezon]

If you purchased the house with the specific intent of making a profit on it, you may be eligible to defer your capital gains under the IRS's "like-kind exchange" rules. You'd have to buy a new fixer-upper within a certain time after selling the first house, and your basis in the new house would be your adjusted basis in the old house (purchase price + cost of materials to improve house + costs of sale). Consult a tax attorney in your area for further information on whether you can take advantage of these provisions.

Alternatively, you can live in the house, take 2 years to rehab & sell it, then exclude $250,000 gain under IRC sec. 125.