Simple vs Compound Interest — When Each Applies

Published May 1, 2026

Simple interest grows only on the principal. Compound interest grows on the principal plus interest already earned, so the curve bends upward over time.

Quick comparison

Idea	Simple	Compound
Typical use	Short bridges, some bonds	Savings, mortgages, investments
Growth shape	Straight line	Accelerating curve
Rule of thumb	Easier mental math	Matches most bank accounts

When simple interest is enough

Very short horizons where compounding rounds away.
Products explicitly quoted as simple (some short-term notes).

When compound interest dominates

Savings accounts, CDs that reinvest, portfolio returns, and most loans where unpaid interest capitalizes.

Use the Interest Calculator to compare simple vs compound scenarios with the same rate and horizon, then read What Is Compound Interest? for the full formula walkthrough.

Simple interest grows only on the principal. Compound interest grows on the principal plus interest already earned, so the curve bends upward over time.

Quick comparison

Idea	Simple	Compound
Typical use	Short bridges, some bonds	Savings, mortgages, investments
Growth shape	Straight line	Accelerating curve
Rule of thumb	Easier mental math	Matches most bank accounts

When simple interest is enough

Very short horizons where compounding rounds away.
Products explicitly quoted as simple (some short-term notes).

When compound interest dominates

Savings accounts, CDs that reinvest, portfolio returns, and most loans where unpaid interest capitalizes.

Use the Interest Calculator to compare simple vs compound scenarios with the same rate and horizon, then read What Is Compound Interest? for the full formula walkthrough.