What Is the Interest Calculator?
This tool calculates interest earned or payable using either the simple interest or compound interest method. It is used for savings accounts, bonds, fixed deposits, and loan cost comparisons in Pakistan and internationally.
The key difference between simple and compound interest is whether accumulated interest itself earns additional interest. For savings products, compound interest works in your favour. For loans, it works against you. If you need to estimate your monthly EMI, you can use our EMI Calculator.
How to Use This Calculator
- Enter your principal amount (starting balance or loan amount).
- Enter the annual interest rate (in percentage, e.g., 12 for 12%).
- Enter the time period in years.
- Select Simple or Compound interest.
- For compound interest, select the compounding frequency (annually, quarterly, monthly, daily).
- Click Calculate to see interest earned and final amount.
Interest Formulas
Simple Interest: SI = P × R × T ÷ 100
Where P = Principal, R = Rate per annum, T = Time in years
Compound Interest: A = P × (1 + r/n)ⁿṭ
Where r = annual rate (decimal), n = compounding periods per year, t = years
Compound Interest = A − P
Worked Examples
Example 1 (Simple): PKR 500,000 at 10% per annum for 3 years.
SI = 500,000 × 10 × 3 ÷ 100 = PKR 150,000 interest. Total: PKR 650,000.
Example 2 (Compound, monthly): PKR 500,000 at 10% per annum compounded monthly for 3 years.
A = 500,000 × (1 + 0.10/12)³⁷ = 500,000 × 1.3482 = PKR 674,100. Compound interest: PKR 174,100 — PKR 24,100 more than simple interest.
Practical Use Cases
- National Savings Certificates (NSC): Pakistan’s National Savings offers certificates at competitive profit rates. Use this to compare NSC returns (simple profit calculation) against bank fixed deposits (compound interest) for the same principal and period.
- Loan cost comparison: When evaluating two loan offers at different rates and compounding frequencies, this tool reveals the true total cost difference, not just the headline rate difference. To analyze full loan repayment for property, try our Mortgage Calculator.
- Retirement savings projection: Model how PKR 50,000/year invested at 12% compounded annually grows over 25 years to understand the power of compounding for retirement planning, though you should also evaluate the real PKR value after inflation to ensure your purchasing power is protected.
Common Mistakes to Avoid
- Confusing profit and interest in Islamic banking: Pakistan’s Islamic banking products use "profit rate" instead of "interest rate" but the mathematical calculation is similar. This calculator applies the same formula and can be used to estimate Islamic banking returns.
- Using annual rate as monthly rate: A 12% annual rate is 1% per month, NOT 12% per month. Entering 12 in a monthly context overstates interest by 12x.
- Assuming compound interest always beats simple: For periods under 1 year with low rates, compound and simple interest are nearly identical. Compounding’s advantage grows significantly over longer periods and higher rates.
Simple vs Compound Interest: The Difference Grows Exponentially With Time
Simple interest is linear — you earn the same amount every period regardless of accumulated returns. Compound interest is exponential — you earn interest on your previous interest. The gap between the two is small over 1-2 years but becomes enormous over a decade.
Real comparison on Rs. 500,000 at 12% for 10 years:
- Simple interest: Rs. 500,000 × 12% × 10 = Rs. 600,000 interest. Total = Rs. 1,100,000.
- Compound interest (annually): Rs. 500,000 × (1.12)¹⁰ = Rs. 1,552,924. Interest earned = Rs. 1,052,924.
- Difference: Rs. 452,924 — from the same principal, same rate, same time.
This is why compound interest is called the eighth wonder of the world — and why understanding which type your savings account or loan uses is not optional.
How Pakistani Banks Apply Interest — What Product Uses What
- Savings accounts: Typically compound interest, calculated daily but credited monthly or quarterly.
- Fixed deposits (TDR): Simple interest for short tenors; compound for longer tenors. Always confirm before signing.
- Consumer loans (car, personal): Reducing balance — which is a form of compound interest applied monthly on the declining principal.
- Credit cards: Compound interest, applied daily on outstanding balance. At typical rates of 36-42% per annum, an unpaid Rs. 50,000 balance doubles in under 2 years.
- National Savings Certificates (Pakistan): Simple or compound depending on the scheme — Special Savings Certificates compound semi-annually; Defence Savings Certificates pay at maturity (effectively compound).
The Rule of 72: A Mental Shortcut Every Investor Should Know
Divide 72 by your annual interest rate to find roughly how many years it takes to double your money at compound interest:
- At 6%: 72 ÷ 6 = 12 years to double
- At 12%: 72 ÷ 12 = 6 years to double
- At 18%: 72 ÷ 18 = 4 years to double
- At 24%: 72 ÷ 24 = 3 years to double
The same rule works in reverse for debt: at 36% credit card interest, your unpaid debt doubles in exactly 2 years.
Three Mistakes When Comparing Savings Returns
- Comparing nominal and effective rates. A 12% rate compounded monthly is not the same as 12% compounded annually. Monthly compounding yields an effective annual rate of 12.68%. Banks often advertise nominal rates — always ask for the effective rate (EAR).
- Ignoring inflation. A 10% savings return when inflation is 25% is a real loss of 15% in purchasing power. Your real return = (1 + nominal rate) ÷ (1 + inflation rate) − 1.
- Confusing APR and APY. APR (Annual Percentage Rate) is nominal; APY (Annual Percentage Yield) accounts for compounding. For savings products, APY is the number that matters.
Frequently Asked Questions
What is the difference between profit rate and interest rate?
In Pakistan’s Islamic banking context, "profit rate" is the Sharia-compliant equivalent of an interest rate. Mathematically, both are applied the same way to calculate returns or costs on financial products. The legal and religious structure differs, but the calculation mechanics are identical.
Which National Savings product pays the best rate?
Note: All bank profits and savings returns in Pakistan are subject to a mandatory 2.5% Zakat deduction on 1st Ramadan unless you file a CZ-50 declaration. Pakistan’s National Savings offers variable rates that change with government policy. Special Savings Certificates, Regular Income Certificates, and Defence Savings Certificates have different terms and rates. Check the National Savings website for current rates before investing.
Is compound interest halal in Islamic banking?
Traditional compound interest (riba) is not permissible under Islamic finance principles. Pakistani Islamic banks offer Murabaha, Musharakah, and Ijarah-based products that provide returns calculated differently but producing similar economic outcomes for the customer.
How does the SBP policy rate affect savings returns?
Pakistan’s savings and fixed deposit rates track the State Bank policy rate. When SBP cuts rates, bank savings account returns fall. When rates are high (as in 2023–2024), savings and NSC returns are at their most attractive.
📅 Last Updated: April 2026
📋 Based on standard financial mathematics and SBP lending standards
👥 Maintained by AKCalc Team
✍️ Built by Shyraz Habib, creator of AKCalc
✓ Reviewed for accuracy: May 2026
This calculator provides estimates based on current financial rules and may not reflect every individual situation. Please verify important decisions with official sources or a qualified professional.