Compound Interest Calculator
By Talcart · Last updated July 10, 2026
Compound Interest Calculator Guide
Understanding Compound Interest
Basic Formula
- A = P(1 + r)^t
- Where: A = Final amount, P = Principal, r = Interest rate, t = Time
- Example: $1,000 at 5% for 5 years = $1,276.28
With Regular Contributions
- Adds PMT × ((1 + r)^t - 1) / r
- Where: PMT = Regular payment amount
- Example: $1,000 initial + $100 monthly at 5% for 5 years
Compound Interest Calculator
This compound interest calculator projects how a balance grows when interest is earned on both the principal and previously credited interest: $10,000 at 7% compounded annually becomes $19,671.51 in 10 years and $76,122.55 in 30. Add optional monthly contributions and choose daily, monthly, or yearly compounding to model savings accounts, CDs, and long-term investments.
Key facts
- $10,000 at 7% compounded annually grows to $19,671.51 in 10 years and $76,122.55 in 30 years.
- Monthly compounding turns $10,000 at 7% into $40,387.39 over 20 years, versus $38,696.84 with annual compounding.
- Rule of 72: money doubles in roughly 72 / rate years -- about 12 years at 6% (exact: 11.90) and 8 years at 9% (exact: 8.04).
- $100 contributed monthly at 8% grows to $149,035.94 in 30 years from just $36,000 of deposits.
What is the Compound Interest Calculator?
Compound interest is interest calculated on the initial principal plus all interest accumulated in earlier periods, so the balance grows at an accelerating rather than linear pace. It contrasts with simple interest, which pays only on the original principal forever. The growth is exponential: each period's interest becomes new principal for the next period. Compounding frequency -- how often interest is credited, from yearly down to daily -- determines how quickly this snowball effect kicks in, and time is its most powerful input.
How does the Compound Interest Calculator work?
The core formula is A = P(1 + r/n)^(nt): principal P grows by the periodic rate r/n for each of the n x t compounding periods across t years. With regular contributions, the calculator adds the annuity term PMT x ((1 + r/n)^(nt) - 1) / (r/n), which compounds every deposit forward from the period it was made. Frequency matters modestly: $10,000 at 7% for 20 years reaches $38,696.84 compounded annually but $40,387.39 compounded monthly -- a 4.4% difference from frequency alone.
What is the Compound Interest Calculator formula?
- A – future value
- P – initial principal
- r – annual interest rate (decimal)
- n – compounding periods per year
- t – years
- PMT – periodic contribution
Growth of $10,000 With Annual Compounding (No Contributions)
| Annual Rate | 5 Years | 10 Years | 20 Years | 30 Years |
|---|---|---|---|---|
| 4% | $12,166.53 | $14,802.44 | $21,911.23 | $32,433.98 |
| 6% | $13,382.26 | $17,908.48 | $32,071.35 | $57,434.91 |
| 7% | $14,025.52 | $19,671.51 | $38,696.84 | $76,122.55 |
| 8% | $14,693.28 | $21,589.25 | $46,609.57 | $100,626.57 |
| 10% | $16,105.10 | $25,937.42 | $67,275.00 | $174,494.02 |
| 12% | $17,623.42 | $31,058.48 | $96,462.93 | $299,599.22 |
How do you use the Compound Interest Calculator?
- Enter your starting balance.
- Enter your annual interest rate.
- Pick the compounding frequency (daily, monthly, yearly, etc.).
- Optional: add a regular monthly contribution.
- Set the number of years to grow.
Worked example
| Scenario | $10,000 invested at 7%, compounded monthly for 20 years, no contributions |
| Calculation | 10,000 × (1 + 0.07/12)^(12·20) |
| Result | Final value ≈ $40,387.39. |
Common use cases
Tips & best practices
Time is more powerful than rate — start early.
Daily compounding adds little once monthly compounding is in play.
Frequently asked questions
It depends almost entirely on the rate: at 4% compounded annually $10,000 becomes $21,911.23 in 20 years, at 7% it becomes $38,696.84, and at 10% it becomes $67,275.00. Stretch the horizon to 30 years and the 10% case reaches $174,494.02 -- more than 17 times the original stake, purely from reinvested interest.
Simple interest is paid only on the original principal, while compound interest is paid on principal plus every dollar of interest already earned. On $10,000 at 7% for 10 years, simple interest yields $7,000 total, but compounding yields $9,671.51 -- 38% more. The gap widens dramatically with time because compound growth is exponential and simple growth is linear.
More frequent is better, but returns diminish fast beyond monthly. At a 6% nominal rate, annual compounding yields 6.00% effectively, monthly yields 6.17%, and daily yields 6.18% -- the daily-versus-monthly gap is under two hundredths of a percent. Focus on the rate and the time horizon; compounding frequency is a rounding error by comparison.
Divide 72 by the interest rate for a quick estimate (the Rule of 72): at 6% it takes about 12 years (exactly 11.90), and at 9% about 8 years (exactly 8.04). The precise answer is ln(2) / ln(1 + r). This shortcut works well for rates between roughly 4% and 12%, drifting at the extremes.
Enormous over long periods. $100 added monthly at 8% (compounded monthly) grows to $149,035.94 in 30 years, even though total deposits are only $36,000 -- interest supplies the other three-quarters. Contributions matter most early: each dollar deposited in year one compounds for the full 30 years, while a year-29 dollar barely grows at all.
Yes, identically in reverse. Unpaid credit-card balances compound, typically daily, so a balance carrying a 24% APR grows at an effective annual rate of about 27.1% if never paid down. The same exponential math that builds savings inflates debt, which is why paying high-rate balances before investing is almost always the better return.
Most US savings accounts compound daily and credit interest monthly, while CDs commonly compound daily or monthly and mortgages compound monthly. The advertised APY already reflects the account's actual frequency, which is why APY -- not the nominal rate -- is the number to compare across banks. This calculator lets you set the frequency to match any product.