Monthly Interest Calculator
Calculate how monthly compounding grows your savings and investments with our free interest calculator. Monthly compounding is the most common frequency for CDs, investment accounts, and many loans, striking a balance between frequent compounding benefits and practical accounting.
Monthly Compounding in Action
| Starting Balance | Interest Rate | Years | Final Balance | Interest Earned | $10,0004% APR5$12,209.97$2,209.97 $10,0005% APR5$12,833.59$2,833.59 $10,0006% APR5$13,488.50$3,488.50 | $10,000 | 7% APR | 5 | $14,176.25 | $4,176.25 |
Monthly vs Annual Compounding
Monthly compounding earns slightly more than annual compounding because interest starts earning interest sooner. The formula: A = P(1 + r/12)^(12t)
For a $10,000 investment at 5% over 10 years:
- Monthly compounding: $16,470.09
- Annual compounding: $16,288.95
- Advantage: $181.14 extra
Monthly Compound Interest Calculator
``javascript
function calculateMonthlyCompound(principal, annualRate, years, monthlyContribution = 0) {
const monthlyRate = annualRate / 100 / 12;
const months = years * 12;
let balance = principal;
for (let i = 0; i < months; i++) {
balance = (balance + monthlyContribution) * (1 + monthlyRate);
}
const totalContributions = principal + (monthlyContribution * months);
const interestEarned = balance - totalContributions;
return {
finalBalance: balance.toFixed(2),
totalContributions: totalContributions.toFixed(2),
interestEarned: interestEarned.toFixed(2),
effectiveAPY: ((Math.pow(1 + monthlyRate, 12) - 1) * 100).toFixed(3) + '%'
};
}
``
Where Monthly Compounding Is Common
Most CDs compound monthly (though they may pay interest quarterly or at maturity). Investment accounts, bond funds, and 401(k) accounts typically compound monthly. Credit cards also compound monthly—but that works against you, making it important to pay balances in full.