Originally Posted by Roadies_Rok

A couple of points which I have a feeling have been mentioned before but I'll highlight them again.
1) You can probably get extra links from the LBS but the chain has already been installed and the newer and thinner chains do not react well to having the pins pushed out multiple times.
2) If you have put any miles at all on the chain your shifting might suffer if you put new links into the existing chain.
3) This is the most important. It is never a good idea to throw away the former chain before you have laid it out and put the new chain beside it and cut the new chain to size. If you are keeping the same tooth count front and rear this is the best and to me the only way to size a new chain. I had a manager at an LBS I worked at yell at me for keeping the old chain in my workbench whenever I did an R&R on a driveline. The guy later got himself fired but no matter how hard I tried he could never understand why I did it. My suggestion don't be like that guy, good luck, and happy riding.