How do I Count Up?

I use something like y=y+1

So it is calculated every tick

But it seems that the number can somehow jump.

which make my condition let say... if y=15 then do something, doesn't work.

What do you mean jump?

passing the number 15, and maybe some other number.

Is it possible? something like form 10 suddenly to 20 due to lag or memory problem, or somehting.

Well it shouldnt do that provided you are using int or rounded numbers.

Are you sure it isn't continuing to count after hitting 15?

Do you have a capx or screenshot?

I've tested it again... it hits number 15. But probably there's another complication.