GenzeeSimple Interest Calculator
Principal, rate and time — get the flat interest, total amount and monthly equivalent instantly. The formula behind committee loans, some certificates and quick estimates.
Total interest
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What is simple interest?
Simple interest is the most basic way to price the use of money: a fixed percentage of the original principal, charged for each year, with no compounding. Lend PKR 100,000 at 12% simple interest and the interest is 12,000 every single year — it never grows, because it is always calculated on the starting amount. That flatness makes it easy to compute in your head and easy to write into informal agreements, which is why simple interest still governs many personal loans between individuals, some savings certificates' quoted returns, and "flat rate" financing offers.
How to use this calculator
Enter the principal, annual rate and time in years (decimals work — 18 months is 1.5 years). The tool shows the total interest, the final amount, and the interest per month, updating as you type.
The formula
Total = P + Interest
where P is the principal, r the annual rate in percent, and t the time in years. Nothing compounds: doubling the time exactly doubles the interest.
Worked example
Ali lends a relative PKR 100,000 at 12% per year for 3 years on simple terms. Interest = 100,000 × 12 × 3 ÷ 100 = PKR 36,000; the relative repays PKR 136,000, or 1,000 per month in interest if paid monthly. Compare the same loan at 12% compound interest: 100,000 × (1.12)³ = 140,493 — PKR 4,493 more. The gap grows dramatically with time, which is why knowing which interest a deal uses matters more than the rate itself. Our compound interest calculator shows the other side.
Watch out for "flat rate" loans
Some financing offers quote a simple ("flat") rate but collect monthly installments. That combination is sneaky: you pay interest on the full principal for the whole term even though you're repaying it month by month, so the true reducing-balance rate is nearly double the flat rate. A "7% flat" car loan over 3 years costs about the same as a 13% reducing-rate loan. Before signing anything with installments, compare against our EMI calculator's total interest for the same rate — if the flat deal's interest is much higher, that's the trick at work.
Frequently asked questions
When is simple interest used in real life?
Informal personal lending, some savings certificates' quoted profit, short-term trade credit, court-ordered payments, and 'flat rate' consumer financing. Banks' standard loans and deposits use compound/reducing-balance methods instead.
Simple vs compound — which earns/costs more?
For the same rate and term, compound always ends higher, because interest earns interest. The difference is small over months and huge over decades.
How do I calculate simple interest for months or days?
Convert to years: 18 months = 1.5, 90 days ≈ 0.25 (or days ÷ 365 for precision). The tool accepts decimal years.
Why is a flat-rate loan more expensive than it sounds?
Because you pay interest on the full principal for the entire term while simultaneously repaying it. The effective reducing-balance rate is roughly 1.8–2× the flat rate on typical tenures.
Is simple interest halal?
Interest (riba) in lending is prohibited in Islamic finance regardless of whether it's simple or compound. Islamic banks structure financing differently (murabaha, ijarah). This tool describes conventional arithmetic only.