use credit karma, but double-check using turbotax
the "free file" limitations vary widely from one provider to another. just pick one of the tax filing websites that is free for your income level (e.g. credit karma for 2017). if you're concerned about the accuracy of the provider, simply complete your taxes in a name brand provider like turbotax (but don't pay to file) then compare the final numbers to the free software. personally, i complete my taxes in 2-3 different providers every year and compare the results. so far they have always matched, but it gives me some peace-of-mind.