Savings Calculator: The Power of Compound Interest
What is Compound Interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. It's often called "interest on interest" and is the key to growing wealth over time.
The Compound Interest Formula
Future Value = P(1 + r)^n + PMT × [(1 + r)^n - 1] / r
Where:
- P = Initial principal (starting amount)
- r = Interest rate per period
- n = Number of periods
- PMT = Regular contribution per period
Why Compound Interest is Powerful
Albert Einstein reportedly called compound interest "the eighth wonder of the world." Here's why:
- Your money grows exponentially, not linearly
- Time is your greatest asset - start early
- Small regular contributions add up significantly
- Interest earns interest on itself
Using Our Savings Calculator
Our calculator helps you plan your savings by showing:
- Future Value: Total amount after specified time
- Total Contributions: Sum of all money you put in
- Interest Earned: How much your money grew
Example Scenarios
Scenario 1: $1,000 initial + $200/month at 5% for 10 years
- Total contributions: $25,000
- Interest earned: ~$7,000
- Future value: ~$32,000
Scenario 2: $1,000 initial + $200/month at 5% for 30 years
- Total contributions: $73,000
- Interest earned: ~$87,000
- Future value: ~$160,000
Tips for Maximizing Savings
- Start saving as early as possible
- Contribute regularly (automate if possible)
- Seek higher interest rates when safe
- Reinvest interest rather than withdrawing
- Be patient - compound interest takes time
Worked examples
- $1,000 start, $200 per month, 5% for 10 years: you pay in $25,000 and end with about $32,703, which includes about $7,703 of interest.
- $10,000 with no more deposits, 7% for 20 years: it grows to about $40,387.
Compounding frequency
Interest can be added yearly, monthly or daily. More frequent compounding gives slightly more growth. The calculator uses monthly compounding. Savings accounts may compound daily, so the real result can differ by a small amount.
The rule of 72
Divide 72 by the annual rate for a quick estimate of the years needed to double your money. At 6% it takes about 12 years, and at 9% about 8 years.
Inflation and real returns
Prices rise over time, so growth is worth less than it appears. If your account earns 5% and prices rise 3%, your buying power grows by roughly 2% per year. When you plan long-term goals, think about the return after inflation.
Build the base first
Before investing for the long term, keep an emergency fund of a few months of essential expenses in an easily accessible account. This stops you from having to sell investments at a bad time.
Habits that grow savings
- Pay yourself first by setting an automatic transfer on payday.
- Increase your contribution whenever your income rises.
- Avoid high-interest debt, because paying it off is a guaranteed return.
- Check fees on any account or fund you use.
- Be patient. Compounding rewards time more than anything else.
A caution
Interest rates on savings accounts change, and investment returns are not guaranteed. Use the calculator to compare scenarios, and speak with a qualified adviser for personal financial advice.