What is the formula for simple interest?

Simple Interest = Principal × Rate × Time (I = P × r × t). The total amount (A) = P + I = P(1 + rt). For example: $10,000 at 5% for 3 years = $10,000 × 0.05 × 3 = $1,500 interest, total = $11,500. Simple interest does not compound — you earn the same dollar amount of interest each period.

When is simple interest used vs compound interest?

Simple interest is used for: short-term loans, US Treasury bills, auto loans in some countries, and informal lending. Compound interest applies to: mortgages, savings accounts, credit cards, investment returns, and most long-term financial products. Most modern financial products use compound interest — always check which applies.

How does Islamic finance handle interest?

Islamic finance (Shariah-compliant) prohibits riba (interest) entirely. Instead of interest-bearing loans, it uses structures like Murabaha (cost-plus financing), Ijara (leasing), and Musharaka (profit-sharing). Sukuk (Islamic bonds) generate returns through asset ownership rather than interest. Islamic banking has significant presence in Malaysia, UAE, Pakistan, Saudi Arabia, and the UK.

Simple Interest Calculator — I = PRT Formula (vs Compound Interest)

Simple Interest Calculator

Calculate simple interest using I = P × r × t and compare it to compound interest. See exactly how much compound interest earns over simple interest across different time periods.

📐 Simple Interest: I = P × r × t (used for short-term loans, treasury bills globally). Compound: A = P(1+r)^t (savings, mortgages). Islamic finance uses different structures (murabaha, sukuk).

Principal ($)

Annual Rate (%)

Time Period

Time Unit

Quick Answer

$10,000 at 5% for 10 years: Simple interest = $5,000 (total $15,000). Compound interest (annual) = $6,289 (total $16,289). Compound earns $1,289 more — with the gap growing exponentially over longer periods.

Simple vs Compound Interest: Where Each Is Used

Product / Context	Type	Where Common
Treasury Bills (T-Bills)	Simple	🇺🇸 US, 🇬🇧 UK, 🇦🇺 Australia
Short-term personal loans	Simple	Worldwide (micro-lending)
Credit cards	Compound (daily)	Worldwide
Mortgages / Home loans	Compound (monthly)	Worldwide
Savings accounts	Compound (daily/monthly)	🇺🇸 US, 🇬🇧 UK, 🇨🇦 Canada, 🇦🇺 AU
Fixed deposits / CDs	Simple or Compound	Varies by institution
Islamic finance (Murabaha)	Neither (profit margin)	🇲🇾 Malaysia, 🇦🇪 UAE, 🇸🇦 Saudi Arabia

Simple Interest Calculator

Quick Answer

Simple vs Compound Interest: Where Each Is Used

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