In AP Business, compound interest is interest calculated on both the original amount you saved (the principal) and the interest that money has already earned, so your savings grow faster over time the longer you leave it alone.
Compound interest is interest that earns interest. You put money in a savings account, it earns interest, and then that interest gets added to your balance. Next time around, you earn interest on the bigger balance, not just your original deposit. Over months and years, this snowballs.
Think of it as the opposite of simple interest. Simple interest only ever pays you on your starting amount. Compound interest keeps stacking earnings on top of earnings, so the growth speeds up the longer you wait. This is exactly why financial institutions like banks and credit unions advertise savings accounts, money market accounts, and certificates of deposit as ways to grow your money. In AP Business, compound interest is the engine behind why saving early for a car, a home, or college tuition (EK 3.1.A.2) pays off so much more than saving late.
Compound interest lives in Unit 3, Topic 3.1 (Saving for Future Purchases). It directly supports [AP Business 3.1.C], where you develop or evaluate a savings plan, because the whole point of choosing one savings vehicle over another (EK 3.1.C.2) is comparing how your money grows. A savings account that compounds is more attractive than stuffing cash under a mattress, which earns nothing.
It also ties into [AP Business 3.1.B] and inflation. Compound interest helps your savings grow, but inflation erodes purchasing power at the same time (EK 3.1.B.2). If your account compounds at a rate below inflation, your money technically grows in dollars but buys less in the future. Understanding that tug-of-war is exactly what a savings-plan FRQ wants you to weigh.
Keep studying AP Business with Personal Finance Unit 3
Visual cheatsheet
view galleryInterest (Unit 3)
Plain interest is the price paid for using money. Compound interest is just interest that keeps getting reapplied to a growing balance, so understanding basic interest is step one before the compounding snowball makes sense.
Saving (Unit 3)
Compound interest is the reward for saving instead of spending. The earlier and longer you save, the more rounds of compounding you get, which is why time matters as much as the amount you set aside.
Opportunity Cost (Unit 3)
Every dollar you spend today is a dollar that could have compounded for years. Compound interest puts a real number on the opportunity cost of not saving.
Inflation under PESTEL factors (Unit 3)
Compound interest grows your money, but inflation shrinks what it can buy (EK 3.1.B.2). Comparing your compounding rate to the inflation rate tells you whether your savings are actually getting ahead.
Compound interest shows up in Unit 3 questions about saving and evaluating savings plans. On multiple choice, expect stems that ask why one savings vehicle grows faster than another, or that test whether you understand that earnings get added back into the balance. On a savings-plan FRQ tied to [AP Business 3.1.C], you may need to explain why starting to save early matters, or weigh a savings option against inflation (EK 3.1.B.2). What you actually do with the term: use it to justify a recommendation. Show that you understand more time and compounding equals more growth, then factor in PESTEL forces like inflation to give a realistic answer.
Simple interest only pays you on your original principal, so a $1,000 deposit at 5% earns exactly $50 every year. Compound interest pays you on principal plus all the interest already earned, so year two earns interest on 1,000. Over time, compound interest pulls ahead, and the gap widens the longer you leave the money in.
Compound interest is interest earned on both your original deposit and the interest that money has already earned.
The longer you let savings sit, the faster they grow, because compounding builds on a larger balance each cycle.
Compound interest is the main reason saving early for big goals like college or a home (EK 3.1.A.2) beats saving late.
When you evaluate a savings plan under [AP Business 3.1.C], compound interest is what makes one savings vehicle grow faster than another.
Inflation works against compound interest, so compare your compounding rate to the inflation rate to see if your money is really getting ahead.
Compound interest is interest calculated on both your original savings (the principal) and the interest you've already earned. It appears in Unit 3, Topic 3.1, as a key reason savings grow over time.
Yes, for someone saving money, compound interest is better because it pays you on a growing balance instead of just your original deposit. The advantage gets bigger the longer you leave the money untouched.
Simple interest only ever pays on your starting principal, so a fixed deposit earns the same dollar amount each year. Compound interest reapplies interest to principal plus past earnings, so each year you earn slightly more than the last.
Not automatically. Compound interest grows your money, but inflation erodes purchasing power (EK 3.1.B.2), so if your compounding rate is below the inflation rate your savings buy less in the future even as the dollar amount rises.
Because compounding builds on itself, more time means more cycles of earning interest on interest. Saving early for goals like a car, home, or college tuition gives your money far more rounds to snowball than saving the same amount later.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.