By Jozsef Huszar • Updated: October 25, 2026
A compound interest calculator shows what time, rate and regular deposits can do to a balance, and the best tool depends on whether you are saving, investing or drawing money down. We reviewed eight online calculators, compared the inputs and outputs of each, and ran one shared example through standard compound-interest math. Research date: October 25, 2026. Tool details come from each provider’s own calculator page, and the dollar figures come from our own calculations. If you want the basics of how compound interest works first, read that, then use this guide to choose a tool.
Quick comparison
Here are all eight calculators as we recorded them on the research date: what each one is for, the inputs it needs, what it returns and how FDIC insurance applies. Check the Key Inputs column first. It shows whether a tool handles regular deposits, withdrawals or only a one-time lump sum. Each tool name links to the calculator itself.
| Provider / Calculator | Primary Use | Key Inputs | Output / Decision Support | FDIC Insured |
|---|---|---|---|---|
| Fidelity Bank – Compound Interest Calculator | Estimate how an initial investment may grow over time through compound interest at different rates and compounding frequencies. | Initial investment amount ($0–$10,000,000), annual interest rate (0%–20%), and investment period (1–50 years). | Displays projected investment growth and compares annual percentage yields (APYs) for yearly, quarterly, monthly, and daily compounding. Illustrative estimates only; actual returns vary, and higher-return investments generally involve greater risk. | Not applicable to the calculator. Fidelity Bank is FDIC-insured; eligible deposits are backed by the full faith and credit of the U.S. Government, subject to applicable coverage limits. |
| NerdWallet – Compound Interest Calculator | Estimate how savings or investments may grow through compound interest over time, with or without recurring contributions. | Initial deposit, years of growth, estimated annual rate of return, compounding frequency, contribution amount, and contribution frequency. | Calculates projected total balance, principal contributions, and interest earned. Allows users to compare different rates, compounding frequencies, time periods, and contribution strategies. Investment returns are hypothetical and may fluctuate; savings account rates can change. | Not applicable to the calculator. NerdWallet is not a bank; FDIC insurance may cover eligible deposits held at participating FDIC-insured banks, subject to applicable limits. Investment products are not FDIC-insured. |
| NerdWallet – Interest Calculator | Estimate how savings account balances grow over time through interest and recurring contributions. | Starting balance, contribution amount, time to grow (years), annual interest rate, compounding frequency, and contribution frequency. | Calculates projected total balance, principal contributed, and interest earned. Helps compare different interest rates, time periods, compounding intervals, and savings contribution strategies. Results are estimates; actual rates and earnings may vary. | Not applicable to the calculator. NerdWallet is not a bank. Eligible deposits held at participating FDIC-insured banks may be insured subject to applicable limits. Brokerage investments are not FDIC-insured. |
| Fidelity Bank – Accumulate Savings Calculator | Project how savings or investments may grow over time with recurring contributions and compound returns. | Starting balance, years to save, annual rate of return, additional contribution amount, contribution frequency, and compounding frequency. | Shows projected balance by year and estimated accumulated savings or investment value. Helps compare contribution amounts, saving periods, and assumed rates of return. Results are hypothetical; investment returns are uncertain and may involve loss of principal. | Not applicable to the calculator. The page identifies Fidelity Bank, but its exact FDIC status should be verified independently. FDIC insurance applies to eligible deposits, not investment returns or calculator projections. |
| Investor.gov (SEC) – Compound Interest Calculator | Estimate how an investment may grow through compound interest and optional monthly contributions or withdrawals. | Initial investment, monthly contribution or withdrawal, investment period in years, estimated annual interest rate, interest-rate variance range, and compounding frequency (annually, semiannually, quarterly, monthly, or daily). | Projects potential investment growth under different interest-rate assumptions and compounding frequencies. Helps compare long-term growth scenarios. Results are estimates and do not guarantee investment returns. | Not applicable. Investor.gov is an educational website operated by the U.S. Securities and Exchange Commission (SEC), not a bank. FDIC insurance applies to eligible bank deposits, not investments or calculator projections. |
| Bankrate – Compound Interest Calculator | Estimate how savings grow over time through compound interest and recurring contributions. | Current savings balance, years to save, annual rate of return (APY), additional contribution amount, contribution frequency, and compounding frequency. | Calculates projected ending balance, total contributions, and interest earned; includes a growth chart. Helps compare savings rates, contribution amounts, time horizons, and compounding options. Results are estimates; savings APYs can change over time. | Not applicable to the calculator. Bankrate is not a bank. Eligible deposits held at FDIC-insured banks may be insured subject to applicable limits; calculator projections are not insured. |
| SmartAsset – Investment Calculator | Understand compound interest and estimate how savings or investments may grow over time. | Principal or investment balance, interest rate, investment period, and compounding frequency. | Explains compound versus simple interest and illustrates how compounding frequency affects growth. Includes educational examples and links to an investment calculator and financial advisor matching service. | Not applicable to the educational article. SmartAsset is not a bank, and its advisor-matching service does not hold customer deposits. FDIC insurance applies to eligible deposits at insured banks, not investments or projected returns. |
| The Calculator Site – Compound Interest Calculator | Project how savings or investments may grow through compound interest, with options for recurring deposits and withdrawals. | Initial investment, annual interest rate, compounding frequency, investment period in years and months, contribution or withdrawal amount, contribution frequency, and optional annual deposit increases. | Calculates future investment value, total interest earned, ending balance, effective compounded rate, overall rate of return or time-weighted return, and estimated time to double the investment. Provides monthly and yearly projections and a year-by-year breakdown. Results are illustrative and do not guarantee returns. | Not applicable. The Calculator Site is a financial tools website, not a bank. FDIC insurance applies to eligible deposits at FDIC-insured banks, not investment balances or projected returns. |
Notes:
¹ Compound-interest tools produce estimates; actual results depend on the account’s APY or investment return, fees, taxes, deposit timing, and withdrawal behavior.
² FDIC status: these are educational calculators, not deposit products, so FDIC insurance is not applicable.
³ Links: add the calculator’s current URL to the first column before publishing.
⁴ For deposit products, confirm whether the advertised rate is APY, which already reflects compounding.
Six of the eight tools accept recurring contributions: both NerdWallet calculators, Fidelity Bank’s Accumulate Savings Calculator, Investor.gov, Bankrate and The Calculator Site. Two of those, Investor.gov and The Calculator Site, also handle withdrawals. Fidelity Bank’s Compound Interest Calculator and SmartAsset cover a single starting balance, so they fit lump sums and learning better than a monthly saving plan.
How we chose and what protection applies
We used the eight calculators in our research file as the final list. They come from a bank (Fidelity Bank), comparison and personal-finance sites (NerdWallet, Bankrate and SmartAsset), a regulator’s education site (Investor.gov, operated by the U.S. Securities and Exchange Commission) and a general financial-tools site (The Calculator Site). We compared what each tool asks for, what it returns and which situations it was built for. We did not rank providers by popularity or by how polished the page looks. A plain tool with the right inputs beats a pretty one that cannot take monthly deposits.
Protection depends on where your money sits, not on the calculator. FDIC insurance covers deposits at insured banks, up to $250,000 per depositor, per insured bank, per ownership category. A calculator is not a deposit product, and its projection is not insured. Brokerage investments are not FDIC-insured deposits either. If you plan to test a savings rate, how FDIC insurance works explains the limits before you move money.
What a typical saver looks like
To compare tools, we need one shared example: a $10,000 starting balance and $200 added at the end of every month. We tested three annual yields. The first is 0.38%, the FDIC’s national average savings rate for July 2026. The second is 4.00%, our illustrative high-yield savings rate, which sits inside the 3.50% to 4.50% APY range that MoneyLion reports for competitive accounts. The third is 7.00%, a hypothetical investment return that no one can guarantee.
We treated each rate as an annual yield and converted it to a monthly rate, so compounding is already built in. Interest accrues on the opening balance each month, and then the deposit is added. You can copy this setup into any calculator in the table, then change the rate to match your account.
Two details deserve a warning. First, most calculators let you choose whether deposits land at the start or the end of each period, and a start-of-month deposit earns slightly more. Second, the 4.00% and 7.00% yields are scenarios, not forecasts. Think of the three columns as a floor, a typical high-yield savings case and an optimistic investing case, and replace them with your own account’s APY or your own return assumption.
What it earns in real life
Table 2 shows the balance after 1, 5, 10 and 30 years for each rate. We used the standard 1-, 5- and 10-year checkpoints and added 30 years, because compounding shows its real strength only after the first decade. We calculated each rate separately and show the amount you put in, including the $10,000 start, so you can see how much comes from interest.
| Horizon | Total you put in | At 0.38% | At 4.00% | At 7.00% |
|---|---|---|---|---|
| 1 year | $12,400 | $12,442 | $12,844 | $13,176 |
| 5 years | $22,000 | $22,304 | $25,402 | $28,265 |
| 10 years | $34,000 | $34,844 | $44,142 | $53,882 |
| 30 years | $82,000 | $87,449 | $169,488 | $310,013 |
The 30-year row is the one to remember. At 7.00%, you put in $82,000 and end with $310,013, so interest supplies $228,013. At 4.00%, the same deposits reach $169,488. At the 0.38% national average, they reach just $87,449. After 10 years the pattern is already visible: $44,142 at 4.00% against $34,844 at 0.38%, on $34,000 contributed. Remember that 7.00% is a hypothetical return, while savings yields can change.
Notice also how little the first year tells you. After 1 year the three columns sit within $734 of each other ($12,442 to $13,176), so a short test can make a poor account look almost as good as a strong one. The gap becomes large only as years pass, which is why long horizons are the right way to judge an account or an investment plan.
The rate matters, but so does when you start. The next table prices that delay.
What happens if you miss the conditions
Compound growth rests on two conditions: you start early, and the rate holds. Table 3 shows the cost of waiting. The $10,000 starting balance stays invested from day one, but the $200 monthly deposits begin after 5 or 10 years, and we measure the balance after 30 years at both the 4.00% and 7.00% rates.
| When the $200 deposits start | Balance at 4.00% | Lost vs. day one | Balance at 7.00% | Lost vs. day one |
|---|---|---|---|---|
| Day one | $169,488 | – | $310,013 | – |
| After 5 years | $134,204 | $35,284 | $232,731 | $77,282 |
| After 10 years | $105,202 | $64,286 | $177,630 | $132,383 |
Waiting 10 years costs $64,286 at 4.00% and $132,383 at 7.00%, even though you skip only $24,000 of deposits. Interest on early deposits has the longest time to build on itself, so the first years carry more weight than the last. The rate condition matters too. If a 4.00% savings rate slid to 0.38% after five years, the 10-year balance would be $38,001 instead of $44,142, a gap of $6,140. Both Bankrate and NerdWallet note that savings rates can change, so recheck your rate from time to time.
With the cost of delay clear, the remaining question is which calculator suits your plan.
Which one fits you
You have one lump sum
Use Fidelity Bank’s Compound Interest Calculator. It takes an initial amount, an annual rate and a period of 1 to 50 years, then compares APYs for yearly, quarterly, monthly and daily compounding. In our math, $10,000 at a 4.00% yield grows to $32,434 in 30 years, and at 7.00% it grows to $76,123. The compounding frequency matters less than rate or time: at a 5.00% nominal rate, $10,000 grows to $16,289 in 10 years with annual compounding and $16,487 with daily compounding, a gap of $198.
You save every month
Use Bankrate’s compound savings calculator, the two NerdWallet calculators or Fidelity Bank’s Accumulate Savings Calculator. All four accept a contribution amount and frequency. Bankrate asks for an APY, which matches the rate on a bank statement, so it suits deposit accounts. NerdWallet’s Interest Calculator is aimed at savings balances, while its Compound Interest Calculator covers savings or investments, and Fidelity’s tool shows the projected balance year by year. In our example, $200 a month at 4.00% reaches $44,142 after 10 years on $34,000 contributed.
You invest or plan to draw money down
Use Investor.gov or The Calculator Site. Investor.gov, operated by the SEC, accepts monthly contributions or withdrawals and an interest-rate variance range, so you can test several return paths. The Calculator Site adds annual deposit increases, a year-by-year breakdown and an estimate of the time needed to double an investment. By our math, money doubles in about 10.2 years at 7.00% and about 17.7 years at 4.00%. Treat any projection as an estimate, because neither tool guarantees returns.
You want to understand the concept first
Use the SmartAsset page. It explains compound versus simple interest and shows how compounding frequency changes growth, but it has no contribution field, so it works best as a primer. Our numbers show why the distinction matters: $10,000 at 4.00% earns simple interest of $12,000 over 30 years, ending at $22,000, but compound interest ends at $32,434, which is $10,434 more.
Choose by question: Fidelity Bank’s calculator for a lump sum, Bankrate or NerdWallet for monthly saving, and Investor.gov or The Calculator Site if withdrawals matter. Run the same inputs through two tools once, and if the totals differ by more than a few dollars, check deposit timing and whether each tool expects a nominal rate or an APY.
What we did not cover
We did not cover taxes, account fees, inflation, tax-advantaged accounts such as retirement plans, bank bonuses or the current APY of any specific account. Real results depend on all of those, and our research notes say so directly. We also left out the advisor-matching service linked from the SmartAsset page. We did not run our example through every calculator, so tool descriptions reflect each page as recorded on the research date. Savings rates in particular can change at any time, so check your bank’s current APY before you plan around it. We also did not test how each page handles very large or very small inputs, and we did not compare mobile layouts. Those details matter less than choosing a tool that accepts the inputs your plan actually needs.
Frequently Asked Questions
Should I enter an APY or an interest rate into a compound interest calculator?
Enter whichever the calculator asks for, and know the difference. APY already reflects compounding, so Bankrate’s calculator asks for it. A nominal rate does not. For example, a 5.00% nominal rate compounded daily equals an APY of about 5.13%. For bank products, confirm whether the advertised rate is an APY.
Why do two calculators show different totals for the same inputs?
Small differences usually come from deposit timing, compounding frequency or how a tool treats the rate. Our own example adds each $200 deposit at the end of the month, while a calculator that adds it at the start of the month will show a slightly higher balance. Check each tool’s settings before you compare results.
Do these calculators include taxes and fees?
Our research notes say actual results depend on the account’s APY or investment return, fees, taxes, deposit timing and withdrawal behavior, and none of the eight tools lists taxes or account fees among its key inputs. To approximate fees, subtract the expected annual fee from the rate you enter, or run a lower rate.
Can I use a savings calculator to project stock-market returns?
You can enter any rate, but the result is a smooth hypothetical line, while real returns fluctuate. Investor.gov’s calculator includes an interest-rate variance range for this reason, and Fidelity Bank’s tool notes that higher-return investments generally involve greater risk. Run several rates instead of relying on one.
Methodology and last update
This guide was researched on October 25, 2026. We took each calculator’s purpose, inputs and outputs from its own page, took savings-rate context from FDIC data and a second published source, and calculated every balance ourselves using monthly compounding. We update the article monthly, or sooner if a tool changes. The content is general information and not personalized financial advice.