here is what you need.
1. determine how many blocks were generated over the last 24 hours because advertised block time are not always true and for most coins the number of blocks per days is fairly consistent except for those with screwed up difficulty adjustment algorithms.
2. then calculate what the btc or dollar volume of the coin on a daily basis. (How much wealth does the coin produce in 24 hours)
3. Add your hashing power to the current network hash for the coin
4. divide your hashing power by (network_hash + your hash) and you'll get a %
5. take that % and multiply the daily coin yield by your percentage
there's you answer.
now pray for the following:
1) the coin does not drop in value
2) someone else does not jump in and add a lot of hash like you have because that will drive your profitability down.
3. Just join
http://smarterhash.com if you're mining scrypt coins and have all these calculations for you constantly on over 50 scrypt coins - because what is most profitable changes all the time - as in dozens of time per day.
by the way we offer a 30 day money back guarantee - you will be more profitable. stop fumbling around in the dark, Smarterhash will open your eyes.
best of luck