Compound Interest Calculator
See exactly how your money grows. Daily, weekly, monthly, or yearly compounding — with regular contributions, annual increases, and live updates as you adjust. Real math, no signup, no nonsense.
Currency
Initial investment
Interest rate
Compound frequency
Time period
Regular contributions
Future value
$6,416.79
Total interest earned
$1,416.79
Total contributions
$0.00
Effective annual rate
5.12%
Time to double
13y 11m
Growth chart
Yearly breakdown
| Year | Start | Contributions | Interest | End |
|---|---|---|---|---|
| 1 | $5,000 | — | $256 | $5,256 |
| 2 | $5,256 | — | $269 | $5,525 |
| 3 | $5,525 | — | $283 | $5,807 |
| 4 | $5,807 | — | $297 | $6,104 |
| 5 | $6,104 | — | $312 | $6,417 |
The math
Why compounding matters
Compound interest is the single most important concept in personal finance. Albert Einstein supposedly called it the eighth wonder of the world. What makes it powerful: each period's interest joins the principal, so the next period's interest is calculated on a slightly bigger number. Over decades, this exponential growth is the difference between a comfortable retirement and a stressful one.
The formula is A = P(1 + r/n)nt — but the practical insights are simpler: contribute regularly, start early, and let frequency work for you. Daily compounding beats monthly. Monthly beats yearly. A $5,000 investment at 5% for 30 years grows to $22,400 with yearly compounding — but $22,469 with daily compounding. Small difference at low rates, huge difference at higher rates or longer terms.
This calculator handles every realistic scenario: deposits and withdrawals, annual contribution increases (to model salary raises), partial reinvestment (for yield farming or strategic withdrawal strategies), and weekday-only compounding for trading-day-based products. The growth chart shows you visually where your future balance comes from: principal, contributions, or earned interest — and which one dominates over time. Usually, after year 15-20, interest pulls ahead of everything else. That's when compounding really starts to work.
Frequently asked
Questions & answers
What is compound interest?
Compound interest is interest earned on both your original principal and on the interest already accumulated. Unlike simple interest (which only pays on the principal), compound interest grows your money exponentially because each period's interest joins the principal for the next period. The more frequently the interest compounds, the faster your money grows — daily compounding produces more than monthly, monthly more than yearly.
What's the difference between daily and monthly compound interest?
Daily compound interest calculates and adds interest to your balance 365 times per year (or 252 times if you only count trading days). Monthly compounding does it 12 times. With the same nominal interest rate, daily compounding produces a slightly higher final balance because each day's interest immediately starts earning more interest. The effect is small for low rates but significant over long periods or at high rates.
What's the formula for compound interest?
A = P(1 + r/n)^(nt), where A is the final balance, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest compounds per year, and t is the time in years. With regular contributions, the formula adds a future-value-of-annuity term: PMT × [((1 + r/n)^(nt) − 1) / (r/n)]. This calculator iterates period-by-period so it handles arbitrary contribution frequencies, annual increases, and partial reinvestment correctly.
What is the effective annual rate (EAR)?
The effective annual rate is the actual percentage your money grows in a year, accounting for compounding. A 5% nominal rate compounded monthly produces an EAR of 5.12%; compounded daily, 5.13%. EAR is the apples-to-apples way to compare savings accounts and investment products with different compounding frequencies.
How does the "Rule of 72" relate to this calculator?
The Rule of 72 estimates how long it takes money to double at a given rate: 72 / interest rate ≈ years to double. At 6%, that's ~12 years; at 9%, ~8 years. This calculator computes the exact time-to-double using the actual compound math (not the rule-of-thumb approximation) and shows it as a top-line metric.
What's the "reinvest rate" in daily mode?
Some investment strategies don't fully reinvest every period's interest — for example, you might pay yourself half the daily yield and let the other half compound. The reinvest rate (0-100%) controls what fraction of each period's interest joins the balance. At 100% you get pure compounding; at 0% it behaves like simple interest. Most realistic for traders, crypto staking, or yield farming.
Why offer weekdays-only daily compounding?
Markets are closed on weekends, so some financial products (margin interest, certain dividend strategies, money market funds) only accrue interest on trading days — typically 252 per year. Toggling "weekdays only" models this. For standard savings accounts that pay daily interest including weekends, leave it off.
How accurate is this calculator?
The math iterates period-by-period using full precision — no rounding shortcuts. For a typical compound interest scenario, results match published bank disclosures to within fractions of a cent. The calculator handles edge cases (zero rate, no time, withdrawals exceeding balance) gracefully. That said, real-world returns depend on tax treatment, fees, and rate changes — this is a math tool, not financial advice.
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