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.
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.
- 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.
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.
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?
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