Interest Calculator

Live simple ↔ compound twin for a single principal, with compound-advantage peel, year-path strip, and EAR peel.

Educational interest sketch only. Not investment, loan, tax, or product advice. Confirm quotes with a lender or prospectus.

By Ahmet C. Toplutaş·Site owner & editor · Finance tools

Last updated May 21, 2026 · Reviewed May 21, 2026 · Planning estimates only - not tax, medical, or investment advice

Simple ↔ compound twin

Simple interest grows only on principal. Compound interest earns on accumulated interest at your chosen frequency.

This page's framing is a simple ↔ compound twin, with a compound-advantage peel, a year-path strip, and an EAR peel. It is not the compound calculator's drip-vs-lump board, not the TVM five-key hub, and not a loan amortization schedule.

Decision framing: “For this principal and term, how much does compounding add versus simple interest?”

Educational interest sketch only. Not investment, loan, tax, or product advice. Confirm quotes with a lender or prospectus. See our disclaimers.

Compound-advantage peel

Advantage is compound interest minus simple interest. As a percent of simple interest, it shows how large the compounding edge is relative to the linear path. Longer terms and higher rates usually widen it.

Year-path strip

The strip shows simple and compound balances along the term so the twin is not only an endpoint. Short terms list each year; longer terms sample milestones through the full horizon.

Tip: load Savings 10y, then switch frequency from annual to daily and watch the advantage and EAR move.

EAR / APY peel

Effective annual rate converts nominal annual rate and compounding frequency into a one-year growth equivalent: (1 + r/n)^n − 1. It is literacy for comparing schedules, not a substitute for a product's disclosed APY after fees.

Core relations

Simple close, compound close, and EAR.

Simple: A = P(1 + r t) I = P r t Compound: A = P(1 + r/n)^(n t) EAR = (1 + r/n)^n − 1 advantage = I_compound − I_simple

Example: $10,000 at 5% for 10 years, monthly compounding → compound balance above the simple path; EAR sits slightly above 5%.

Where this hands off

Sibling boards for deposits, TVM solves, rate finding, and loan payments.

Compound interest (drip vs lump, frequency stress with contributions)
Finance (TVM) (FV / PV / PMT / rate / N)
Interest rate / loan
Terms: finance glossary

Worked scenarios

Scenario A: Savings 10y. $10,000 at 5% for 10 years, monthly. Read the twin and advantage; year path shows the gap opening after the early years.

Load Daily edge: higher rate and daily compounding push EAR and advantage harder on a smaller principal.

Scenario B: Short term. Three years keeps the compound edge smaller; useful for seeing when simple is “close enough” for a napkin estimate.

Scenario C: Long annual. Twenty years at annual compounding still beats simple; milestone path samples the long horizon.

Scenario D: Need deposits. Hand off to compound interest when recurring contributions matter.

Common mistakes

Applying a compounding frequency to the simple interest line.
Comparing nominal APR to EAR without converting.
Forgetting that this board has no recurring deposits or loan fees.
Using this twin instead of the TVM board when you need to solve for PMT or N.
Treating EAR as a guaranteed investment return after taxes and fees.

How to use this board

Enter principal, annual rate %, and years.
Pick compounding frequency (simple path ignores it).
Read the simple ↔ compound twin and advantage peel.
Scan the year-path strip and EAR peel.
Share writes board state; typing does not rewrite the address bar.

When not to stop at this sketch

Stop here for simple-vs-compound literacy on a single principal. Hand off for deposit drips, full TVM solves, or loan schedules. For real products, read the disclosure.

With contributions: compound interest calculator.
Five-key TVM: finance calculator.
Loan payments: loan calculator.

Frequently asked questions

How does this interest calculator work?

It compares simple interest (I = P·r·t) with compound interest at your chosen compounding frequency. A simple ↔ compound twin shows interest and balances side by side, an advantage peel quantifies the gap, a year-path strip tracks both balances over time, and an EAR peel converts nominal APR plus frequency into effective annual rate.

What is the simple ↔ compound twin?

Simple interest grows linearly with time on the original principal. Compound interest earns interest on accumulated interest. The twin keeps both ending balances and interest amounts visible for the same P, r, and t.

What is the compound-advantage peel?

It is compound interest minus simple interest (and that gap as a percent of simple interest when simple interest is non-zero). Longer terms and higher rates widen the edge.

What is EAR / APY here?

Effective annual rate from nominal annual rate and compounding frequency: (1 + r/n)^n − 1. It is the yearly growth equivalent if you reinvest at that schedule. Product APY disclosures can differ by rounding and fees.

How is this different from the compound interest calculator?

The compound interest page focuses on drip vs lump deposits and frequency stress for a compounding plan. This page owns the simple-vs-compound teaching twin and year-path comparison with no recurring deposits.

How is this different from the finance (TVM) calculator?

TVM solves any of FV, PV, PMT, rate, or N with begin/end timing. This page compares two interest conventions for a single principal over time.

Is this investment or loan advice?

No. It is an educational interest sketch only. Not investment, loan, tax, or product advice. Confirm quotes with a lender or prospectus. See our disclaimers.

Sources

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Methodology & sources

Our finance calculators use standard formulas and common assumptions. Results are estimates and may differ due to fees, taxes, rounding, and lender/provider policies. Use this for planning—not as a quote.

Core sources

Loans hub Finance formulas Editorial policy Corrections Contact

Simple ↔ compound twin

Simple interest grows only on principal. Compound interest earns on accumulated interest at your chosen frequency.

Decision framing: “For this principal and term, how much does compounding add versus simple interest?”

Educational interest sketch only. Not investment, loan, tax, or product advice. Confirm quotes with a lender or prospectus. See our disclaimers.

Worked scenarios

Scenario A: Savings 10y. $10,000 at 5% for 10 years, monthly. Read the twin and advantage; year path shows the gap opening after the early years.

Load Daily edge: higher rate and daily compounding push EAR and advantage harder on a smaller principal.

Scenario B: Short term. Three years keeps the compound edge smaller; useful for seeing when simple is “close enough” for a napkin estimate.

Scenario C: Long annual. Twenty years at annual compounding still beats simple; milestone path samples the long horizon.

Scenario D: Need deposits. Hand off to compound interest when recurring contributions matter.

Common mistakes

Applying a compounding frequency to the simple interest line.
Comparing nominal APR to EAR without converting.
Forgetting that this board has no recurring deposits or loan fees.
Using this twin instead of the TVM board when you need to solve for PMT or N.
Treating EAR as a guaranteed investment return after taxes and fees.

Frequently asked questions

How does this interest calculator work?

What is the simple ↔ compound twin?

What is the compound-advantage peel?

It is compound interest minus simple interest (and that gap as a percent of simple interest when simple interest is non-zero). Longer terms and higher rates widen the edge.

What is EAR / APY here?

How is this different from the compound interest calculator?

How is this different from the finance (TVM) calculator?

TVM solves any of FV, PV, PMT, rate, or N with begin/end timing. This page compares two interest conventions for a single principal over time.

Is this investment or loan advice?

No. It is an educational interest sketch only. Not investment, loan, tax, or product advice. Confirm quotes with a lender or prospectus. See our disclaimers.

Simple ↔ compound twin

Compound-advantage peel

Year-path strip

EAR / APY peel

Core relations

Where this hands off

Worked scenarios

Common mistakes

How to use this board

When not to stop at this sketch

Frequently asked questions

How does this interest calculator work?

What is the simple ↔ compound twin?

What is the compound-advantage peel?

What is EAR / APY here?

How is this different from the compound interest calculator?

How is this different from the finance (TVM) calculator?

Is this investment or loan advice?

Sources

Methodology & sources

Simple ↔ compound twin

Compound-advantage peel

Year-path strip

EAR / APY peel

Core relations

Where this hands off

Worked scenarios

Common mistakes

How to use this board

When not to stop at this sketch

Frequently asked questions

How does this interest calculator work?

What is the simple ↔ compound twin?

What is the compound-advantage peel?

What is EAR / APY here?

How is this different from the compound interest calculator?

How is this different from the finance (TVM) calculator?

Is this investment or loan advice?

Sources

What this number means

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