While joining a contest, 30% of the contest entry is deducted from the Discount Points bucket (as a part of Amount Unutilised).
To view the exact calculation, keep an eye on the alert we display while you're about to finally join the contest.
To keep track of how many discount points have been used up, you can always go to Profile -> My Balance -> My Transactions and check for the entire contest breakup.
In case you need any further help, contact us here.