The rates we display on our home page and in your dashboard are your APY (Annual Percentage Yield). APY is what you end up with after a year, including compounding.
Suppose you deposit $100,000 and your APY is 15%. If you don't make any further deposits or withdrawals, after a year you'll have $115,000.
With Stablegains, your interest accrues daily. The amount you get each day can be calculated using your APR (Annual Percentage Rate), which for a 15% APY would be 13.98%. This means that each day you would receive 13.98% / 365 = 0.038% of your current deposits. The extra interest accruing each day compounds, and on a one year timescale contributes to your ultimate 15% APY.
Here is a handy link to get a better feel for the APR vs APY relationship: aprtoapy.com.