Compound interest calculator
See how a starting balance and monthly deposits grow with interest compounded on interest.
Method: Periodic compounding converted to an effective monthly rateReviewed Oct 2026
Your numbers
$
$
%
yrs
Results
Ending balance
$102,180
After 20 years
Total deposits
$58,000
$10,000 + $200/mo
Interest earned
$44,180
APY 4.594%
Deposits $58,000 (57%)Interest $44,180 (43%)
Balance by year
ContributedGrowthFormula
FV = PV(1 + i)ⁿ + PMT · ((1 + i)ⁿ − 1) ÷ i
With your numbers
FV = $10,000(1 + 0.003750)^240 + $200 · ((1 + 0.003750)^240 − 1) ÷ 0.003750 = $102,180
In plain EnglishStarting with $10,000 and adding $200 a month at 4.50% APR, you reach $102,180 in 20 years. $44,180 of that is interest, and most of it arrives in the later years as interest earns interest.
- 1APY = (1 + APR ÷ k)ᵏ − 14.594%
- 2Effective monthly rate i0.003750
- 3Months n = years × 12240
- 4Starting balance grows to$24,555
- 5Deposits grow to$77,625
- 6Interest earned = FV − deposits$44,180
YearDepositsInterestBalance
1$12,400$510$12,910
2$14,800$1,153$15,953
3$17,200$1,936$19,136
4$19,600$2,865$22,465
5$22,000$3,947$25,947
6$24,400$5,189$29,589
7$26,800$6,599$33,399
8$29,200$8,183$37,383
9$31,600$9,951$41,551
10$34,000$11,910$45,910
11$36,400$14,069$50,469
12$38,800$16,437$55,237
13$41,200$19,025$60,225
14$43,600$21,842$65,442
15$46,000$24,898$70,898
16$48,400$28,206$76,606
17$50,800$31,775$82,575
18$53,200$35,619$88,819
19$55,600$39,749$95,349
20$58,000$44,180$102,180
What is the difference between APR and APY?
APR is the stated annual rate. APY includes the effect of compounding within the year, so it is a little higher.
When are deposits added?
At the end of each month, after that month’s interest is credited.