Permanent hair dye - how often can I use it?

[OhThisIsJustGrape]

usually use semi-permanents but sick of them fading so fast. Dyed my hair using a permanent at home dye the week before Christmas so approx 8 weeks ago, can I do it again yet? Dye has faded quite a bit but still some left on my hair but greys are growing.

Also, may go a shade lighter as although colour looked ok on box it was a touch too dark for me, will this make any difference? It's a dark brown colour.

Your roots might be slightly lighter but that is the same with any regrowth. I dye mine every 5-6 weeks (I use black dye) and it doesn't seem to have a negative effect but I treat my hair well (I use elasticizer, hairfix and argan oil).