I have a domain name registered with register.com for 10 years with domain privacy but i want to transfer it to some other registrar .So if transfer my domain now ,do i need to pay again for 10 years ?
It depends up to you! that for how much time you select the registration period.... the minimum number of years is 1 year!
My domain is registered in 2008 and it has an expiration date in 2018 ..So if i transfer it now i need to pay for 2010-2018...is that true.
You do not need to pay again. You will just need to pay transfer fees and your domain name will be transferred with one more additional year.
Like others have stated, it's just a one year renewal even if you paid multiple years ahead on your previous registrar. That should clear up your concerns!