However national insurance is only 2% above £50,270 so If I was earning £500k it would still be 47% total tax for sole trader vs 57.1 for a company would it not?
You are right it is a mixed bag and ultimately tax can swing back in favour of sole trader as you say when ni drops to 2%
Note if you go the full hog and factor in full lifetime use of funds aligned with pension planning the limited company format can blow the sole trader out of the water at present if for example you make £120k profit - live on 50k cash (possible more if you have spiuse sharholder / employee blah) - add decent wad into pension and leave excess in company to worry about later. Basically higher rate tax need never be paid if your cash needs are moderate and you arent into the millions retained earnings wise.
Ie can you avoid the automatic higher rate tax that applies as sole trsader "if you dont need that cash" and can manage to avoid higher rate tax.
Company format is perfect in that if you earn 40k profit that would be taxed at higher rate as sole trader your company can add all that into your pension (subject to pension limits etc take IFA advise blah) and full sum earned ends up in your pension pot. When you add to pension as sole trader you don''t get any NI reduction so are losing out on the 2%/9% NI you are paying on your tax return.
Another big saving at present is the mismatch on where higher rate tax kicks in!
If your sole trader profit is 58840 - you are nearly 9k into higher rate tax
For limited company at same equivalent profit level - your company will pay £9500 copr tax and your withdrawals IF ALL extracted will be below 50k therefore avoiding ANY higher rate tax - thats a very material saving compared to the nearly 9k with extra 20% added.
For convenience i have ignored the future increase in corp tax.