Financial Readiness
Compounding is interest earning more interest. Given time, it does the heavy lifting in any savings plan.
Official TSP campaign artwork aimed at uniformed services members. Artwork courtesy of TSP via DVIDS.
Compound interest is interest that earns more interest. It is paid on your principal, the money you put in, and on the interest you have already earned. In plain terms, your money earns money, and then that money earns money too.
Two levers drive it: time and rate. Start early, keep adding, and let it run. That is the whole game.
Watch one deposit grow with no new money added. The only added ingredient is time, and that is compounding at work.
Illustrative example from Investor.gov: a one-time $730 deposit at 5 percent, no new money added.
Two levers
Same deposit, same rate. The only added ingredient is time.
Source: Investor.gov (SEC) · St. Louis Fed · figures illustrative
Simple interest pays only on your original deposit. Compound interest pays on the growing balance, so each period starts from a slightly bigger number. Over years, that difference stacks up.
How often interest compounds, daily, monthly, or yearly, changes how fast it grows. More frequent compounding earns a little more. That is why APY, the figure that bakes in compounding, is the number to compare across accounts.
Use the Rule of 72. Divide 72 by your annual rate for a rough number of years to double. At 4 percent, that is about 18 years. At 6 percent, about 12 years. It is an approximation, not a promise, but it is a fast gut check.
Time is the one lever you cannot get back. A dollar saved at 18 has more years to compound than a dollar saved at 28, so it can grow into more, even if the later saver puts in more cash. Junior enlisted service members have an edge few civilians their age have: steady pay and early access to strong savings tools. Starting small now beats starting big later.
The same math that grows your savings can grow a credit card balance. The trick is to point compounding in your favor and shut it off everywhere else.
Saving: Interest earns interest. Automate a deposit each payday and leave it alone. The snowball builds while you do nothing.
Debt: Credit cards can compound against you. Pay the statement balance in full by the due date to shut it off.
Put it to work
Start small now beats starting big later.
Source: CFPB · Military OneSource (SDP) · figures illustrative
Open an account that pays a real APY, like a high-yield savings account, and confirm it is FDIC or NCUA insured. Automate a deposit each payday, even a small one, and leave it alone. Knock out high-interest debt in parallel so compounding is not working against you. Deployed? The Savings Deposit Program pays 10 percent with interest that compounds monthly on balances up to $10,000, a rate civilian accounts rarely match.
You do not have to figure this out alone. Military OneSource offers free financial counseling. Your installation Personal Financial Manager or Counselor is free and in person on base. The DoD Office of Financial Readiness (FINRED) has military money education and tools. Investor.gov from the SEC has a free compound interest calculator, and the CFPB has plain-language answers on saving and borrowing. All are linked in Sources below.
What is the difference between APY and APR?
APY is what you earn, and it includes compounding. APR is the rate you pay to borrow, and it does not include compounding.
Does more frequent compounding really matter?
It helps, but the rate and your time horizon matter more. Compare accounts by APY, which already accounts for compounding frequency.
Is compound interest a sure thing?
Insured deposit principal is protected within the limits, and a positive APY adds interest over time. The APY is variable, though, and inflation can offset some growth. Treat any projection as an estimate.
