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Compound interest calculator

Find out how compound interest can help you grow your savings.

Updated

Compound interest is an effective tool that helps your money grow faster. Unlike simple interest, which is calculated only on the principal amount, compound interest is calculated based on your growing balance, including any interest you’ve already earned. Use this calculator to find out how much you could earn with the power of compound interest.

Calculate your compound interest

How do banks calculate compound interest?

With most savings accounts, interest is calculated every day on your daily closing balance.

Compound interest formula

Here’s the equation that most banks use for savings accounts:

(Daily closing balance) x (interest rate)
365

Interest begins to accumulate on the day of your first deposit. It’s then credited into your account on the last day of each month. If you close your account, your accrued interest is deposited on the day it’s closed.

Any interest awarded to your savings account is typically available for use on the same day it’s credited.

How can I calculate the compound interest?

Compound interest is a complicated calculation that’s often easier left to online calculators designed for that purpose. Still, you can refer to the same formula banks use to calculate your compound interest:

Daily closing balance x interest rate percentage / 365

Say you invest $1,000 with an interest rate of 10% compounded annually for five years. Using the compound interest formula, you’ll find that your initial investment of $1,000 earns $100 after the first year, giving you a total of $1,100.

The total amount yielded for the first year will then earn $110 — 10% of $1,100 — as interest for the next year, bringing your balance to $1,210. This amount then becomes the base for compounding for the third year, and so on. After five years, your initial balance would total $1,610 due to compounding interest alone.

How does compound interest work in technical terms?

Think of compounding as a way of earning interest on your interest. A savings account with ongoing compound interest applies interest to the interest that you’re already paid.

Compound interest differs from simple interest, which is typically associated with loans. For loans, simple interest is calculated on the principal — or the original loan amount — only.

Again, it’s complicated. But we can get an idea of the benefits of compound interest on your savings by analyzing the mathematical formula associated with it:

Screenshot 2015-10-14 10.57.13

Here’s what those letters and annotations represent:

  • A — the future value of your total investment, including earned interest
  • P — your initial deposit amount or principal investment
  • r — the interest rate annually as a decimal
  • n — how often interest is compounded each year
  • t — the number of years the money is invested for

For most savings accounts, your interest is compounded monthly — or 12 times in a year. For long-term savings products, like certificates of deposit, the formula or compounding period may differ.

Case Study: How compound interest helps your savings grow

To better understand the benefits of compound interest, take a look at how one saver’s account grows depending on any number of factors found with your typical savings account.

Here, Miles deposits $5,000 into a standard savings account that pays interest at a rate of 3.5%.

Interest is calculated daily and deposited into the account at the end of each quarter:

Principal (P)Rate (r)Compound (n)Time (t)Interest earned after 1 year
$5,0003.5%41$177.31

At that same rate for the next five years, here’s how much he’ll earn:

Principal (P)Rate (r)Compound (n)Time (t)Interest earned after 5 years
$5,0003.5%45$951.70

If interest is paid annually, here’s where Miles’s interest earnings would stand after five years:

Principal (P)Rate (r)Compound (n)Time (t)Interest earned after 5 years
$5,0003.5%15$938.43

If interest is compounded daily, here’s interest earnings after five years:

Principal (P)Rate (r)Compound (n)Time (t)Interest earned after 5 years
$5,0003.5%3655$956.18

Note that for accurate calculations, you can’t account for any withdrawals or fees deducted from the balance over the period you’re calculating. Adding to your balance also changes your results. We did say it’s complicated.

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Compare savings accounts with compound interest

$
$
months
Name Product Interest rates (APY) Fee Minimum deposit to open Interest earned More info
American Express® Personal Savings High Yield Savings
1.00%
$0
$0
Go to site
View details
Enjoy no monthly fees and a competitive APY with this online-only savings account. Accounts offered by American Express National Bank, Member FDIC.
CIT Bank Savings Builder High Yield Savings Account

0.95% on balances of $25,000+ or set up a direct deposit of $100+ each month
0.79% on balances of $0 to $24,999
$0
$100
Go to site
View details
No account opening or maintenance fees. Daily compounding interest. Earn one of the nation's top rates
Discover Online Savings Account
1.01%
$0
$0
Go to site
View details
Take advantage of a high-interest online savings account with no fees, no minimums and more.
Aspiration Spend & Save Account

1.00% on balances of $0 to $10,000 but you’ll need to be enrolled in Aspiration Plus and make at least $1,000 in debit card purchases a month
$0
$10
Go to site
View details
A spend and save combo account with no monthly service fees, free access to every ATM in the world, unlimited cash back rewards and deposits insured by the FDIC. The Aspiration Spend & Save Account is a cash management account offering of Aspiration Financial, LLC, an SEC-registered broker-dealer. Aspiration is not a chartered bank.
UFB Direct High Yield Savings
0.40%
$0
$100
Go to site
View details
Earn an APY when your balance is higher than $10,000 with this no-monthly-fee savings account.
BBVA Money Market

0.19% on balances of $1,000,000+
0.10% on balances of $100,000 to $999,999
0.05% on balances of $0 to $99,999
$15 per month
(can be waived)
$25
Go to site
View details
Earn a promotional APY for your first 3 months and access your money by ATM, check or bill pay.
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Compare up to 4 providers

Bottom line

A savings account with compound interest can help you reach your financial goals sooner, just for letting your money sit in the account. Most of today’s savings accounts use compound interest, but you should check the terms and conditions because it can help your balance grow much faster than an account with simple interest. Or, you can compare some of our top-rated options to find out what other savings accounts are out there.

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