Solverly

Compound Interest Calculator

Convert between APR and APY across different compounding schedules. Pick an input rate and schedule, then choose an output schedule to see the mathematically equivalent rate. The equivalents table lists all schedules at once.

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6.00000% Monthly (APR) is equivalent to 6.16778% Annually (APY).

All equivalent rates from the input

ScheduleRate
Annually (APY)6.16778%
Semiannually6.07550%
Quarterly6.03005%
Monthly (APR)6.00000%
Semimonthly5.99252%
Biweekly5.99194%
Weekly5.98850%
Daily5.98554%

Annual is APY (effective). Others are nominal APR at the stated compounding frequency.

What this Compound Interest Calculator does

This tool converts an interest rate stated with one compounding schedule into the equivalent rate for another schedule. For example, you can convert 6% compounded monthly (APR) into the equivalent annual yield (APY), or turn an APY into an APR with weekly or daily compounding. The calculator uses the effective-annual-rate framework so all conversions are mathematically consistent.

APR vs. APY in plain language

APR (annual percentage rate) is a nominal rate that assumes a compounding schedule. APY (annual percentage yield) is the effective return over a full year after compounding. If two products have different compounding schedules, compare their APY values: APY puts everything on the same footing.

How the conversion works

  • Convert the input to a single effective annual rate (APY). For a nominal APR with n periods per year: APY = (1 + APR/n)n − 1. If the input is already APY, this step is just the input itself.
  • Convert that APY to the target schedule. For the target with n periods per year: APR = n · ( (1 + APY)1/n − 1 ). If the output is APY, just report the APY.

When to use which schedule

Financial institutions commonly quote checking and savings yields as APY (annual, effective), while loans and cards are often quoted as APR with a specific compounding frequency (monthly, daily, etc.). Use this converter any time you need an apples-to-apples comparison—for example, comparing a daily-compounded savings account against a monthly CD, or evaluating two loans with different compounding schedules.

Practical tips

  • When comparing products, convert both to APY first, then decide.
  • More frequent compounding raises the effective return slightly for a given nominal APR.
  • For short horizons, compounding frequency matters less than the headline rate.
  • APY assumes reinvestment of interest; real-world results can vary with fees, day-count, and timing.

Calculations are estimates for planning and education. Real contracts can use different day-count conventions, fee treatments, or rounding rules that change the exact numbers.

Compound Interest FAQ

What is compound interest?

Compound interest means you earn interest on both your original principal and on the interest previously added. Over time, that “interest on interest” accelerates growth.

How is compound interest different from simple interest?

Simple interest applies only to the original principal. Compound interest applies to principal plus previously earned interest, which generally produces a larger ending balance.

How does compounding frequency affect growth?

More frequent compounding (monthly vs. annual) increases the effective annual yield. For the same APR, monthly > quarterly > annual, and continuous compounding is the theoretical maximum.

What’s the difference between APR and APY?

APR is the stated annual rate without compounding. APY includes compounding effects. The calculator converts your APR and frequency into an effective APY.

Do regular contributions matter?

Yes—consistent deposits (monthly/annual) dramatically increase the ending balance because each contribution gets time to compound.

Can I model inflation?

You can approximate “real” growth by subtracting an inflation rate from the interest rate, or by discounting the ending balance using expected inflation.

What is continuous compounding?

It’s the limit of compounding frequency going to infinity. The balance follows A = P · ert. In practice, monthly or daily compounding is close enough for most cases.

How long until my money doubles?

A quick rule is the Rule of 72: divide 72 by your annual rate (as a %). At 8% annually, money doubles in about 9 years (72 ÷ 8 ≈ 9).

Use cases & examples

Example 1 — One-time investment

Invest $10,000 at 7% APR, compounded annually for 15 years. Ending balance ≈ $27,590 (no additional contributions).

  • Interest earned ≈ $17,590
  • Effective APY (annual compounding) ≈ 7.00%

Example 2 — Monthly contributions

Start with $0, contribute $300/month at 6% APR compounded monthly for 20 years. Ending balance ≈ $139,000.

  • Total contributions ≈ $72,000
  • Growth/interest ≈ $67,000

Example 3 — College fund with annual deposit

Contribute $2,500/year for 18 years at 5% APR, compounded annually. Ending balance ≈ $74,000.

  • Total contributions ≈ $45,000
  • Growth/interest ≈ $29,000