Start with what you have, add a monthly amount, and watch how much of the result is interest.
Future balanceAfter 20 years
You'll have
$196,665
Your deposits
$82,000
Interest earned
$114,665
Deposits
Interest
Year by year
Year
Deposits
Interest
Balance
1
$13,600
$841
$14,441
2
$17,200
$2,002
$19,202
3
$20,800
$3,508
$24,308
4
$24,400
$5,383
$29,783
5
$28,000
$7,654
$35,654
6
$31,600
$10,349
$41,949
7
$35,200
$13,500
$48,700
8
$38,800
$17,138
$55,938
9
$42,400
$21,299
$63,699
10
$46,000
$26,022
$72,022
11
$49,600
$31,346
$80,946
12
$53,200
$37,316
$90,516
13
$56,800
$43,977
$100,777
14
$60,400
$51,380
$111,780
15
$64,000
$59,578
$123,578
16
$67,600
$68,629
$136,229
17
$71,200
$78,595
$149,795
18
$74,800
$89,542
$164,342
19
$78,400
$101,540
$179,940
20
$82,000
$114,665
$196,665
Frequently asked questions
What is compound interest?
Interest earned on both your original money and on the interest already added. Over long periods the interest-on-interest becomes the largest part of the balance.
What is the compound interest formula?
For a single deposit: A = P(1 + r/n)nt, where P is the principal, r the annual rate, n how many times a year interest compounds and t the number of years. With monthly deposits, each deposit grows for the months remaining.
What return should I assume?
High-yield savings accounts and CDs pay a stated rate. For stock index funds, long-run historical averages are often quoted around 7% after inflation and about 10% before, but returns vary a lot from year to year and are not guaranteed.
What is the rule of 72?
Divide 72 by the annual rate to estimate how many years it takes money to double. At 7%, that is about 10 years.