As far I can figure out, if you want to be honest, there is no way to avoid paying car tax for June & July if you tax it now in May for 3 mts. The only month you will avoid is Aug when you come back to tax it in Sept. I had something similar lately when my father was getting a new(er) car but he wouldnt have it for a month. The tax was out on his old car and I wanted to retax it but no way could I pay for just the month, despite ringing the local office who told me I could pay it as arrears as it was week or so into the month at that stage, after going to office, looong queue, got to top to be told I could only pay a month of arrears if I was going to pay for the next three months as well, but as his car would be gone by then that was pointless and they wont transfer tax if less than 3 months o/s either. Got so frustrated with it decided to hell with it, got letter from Tax office then saying Guards would be notified if car not taxed within certain time, sent off letter to Guards with tax letter explaining I had done my best to pay them for the month but no luck. Never heard a word afterwards.