Comparing today's account balance to yesterday's

Good day ,

Guys , help with my EA. Before start trading everyday or before going through each iteration ( on tick ) , I want my code to verify and compare yesterday’s AccountBalance to today’s. If today’s AccountBalance is greater than or equal to 5% than yesterday , then stop trading. Here’s what I thought about it :

    if ( //AccountBalance is >= 5% than yesterday's ) {
      // return;
   } else {
      // starttrading();

But the question is simple , how do I compare it to yesterday’s account balance ? How do I put it in code ?

Any ideas would be highly appreciated.