Too small of cups for plants?

I have my plants in to regular plastic cups at the moment but the tips of their leaves are getting yellow..is this the cause of it bc i need bigger pots now or could it be bc not enough water or too much or other factors?

Also, the reason i am thinking this is bc its not all the leaves or random leaves that are doing this..its starting with the first leaves that came out of the plant then the next ones and so forth so far about 2 sets or leaves are starting to get yellow on about 3 of my plants and i can tell a little on the next set but all the newer leaves don't have yellow..i thought it was nute burn at first but this seems like the most logical

if u have leafs out u need somthing bigger than a plastic cup. the yellowing could be for nutrents burn, or lighting burn

gutter8 said:

if u have leafs out u need somthing bigger than a plastic cup. the yellowing could be for nutrents burn, or lighting burn

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no offense but this isnt true about the cups. I go straight from germination to 18oz plastic party cups, 4 weeks veg under CFL's, then 3 gallon containers for flowering to the end. Never had a problem, but i wouldnt go any longer than 4 weeks MAX