💰 Interest · Principal · Rate · Time · Date to date · Byaj ledger
Simple Interest Calculator
Work out simple interest and total amount for years, months, days or between two dates, or solve for the principal, rate or time. Supports % per year and the Indian byaj / sekda rate (₹ per ₹100 per month), a multi-entry loan ledger with part payments, and a compound interest comparison. Runs privately in your browser.
Calculate
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Simple interest
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Total amount (P + SI)
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Interest per month
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Interest per day
Simple vs compound interest
Year by year
Period
Interest
Total interest
Amount
Compound amount
Loan ledger (byaj khata) with part payments
For money lent or borrowed in several instalments, or repaid in parts. Simple interest runs on the outstanding principal between entries; each repayment clears interest due first, then principal. Uses the rate and day-count above. Saved only in this browser.
Date
Entry
Days
Interest accrued
Interest due
Principal due
This is an arithmetic aid. Banks, courts and lenders may use different day counts, rounding or appropriation rules, and many loans compound or charge penal interest. Check your agreement. Interest above the legal or registered-lender limits in your state may be unlawful to charge.
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Private: All calculations run locally in your browser. Nothing is uploaded.
Simple interest formula
SI = P × R × T ÷ 100, where P is the principal, R the rate in % per year and T the time in years. Total amount A = P + SI = P × (1 + R × T ÷ 100). Example: ₹1,00,000 at 10% for 2 years gives SI ₹20,000 and amount ₹1,20,000.
Principal: P = SI × 100 ÷ (R × T), or P = A ÷ (1 + R × T ÷ 100).
Rate: R = SI × 100 ÷ (P × T).
Time: T = SI × 100 ÷ (P × R) years.
Simple interest for months and days
Convert time to years first. For months, T = months ÷ 12: ₹50,000 at 12% for 9 months is 50,000 × 12 × 0.75 ÷ 100 = ₹4,500. For days, T = days ÷ 365: ₹2,00,000 at 9% for 90 days is ₹4,438.36. Some lenders divide by 360, which gives slightly more interest (₹4,500 here).
Byaj, sekda and date-to-date interest
In many parts of India private loans are quoted as ₹ per ₹100 per month (called sekda, byaj or vaddi rate). ₹2 sekda means ₹2 interest on every ₹100 each month, which is 24% a year. The traditional count takes whole calendar months from the start date and the leftover days at 1/30 of a month. ₹1,00,000 at ₹2 sekda from 15 January to 10 March 2026 is 1 month 23 days, so interest = 1,00,000 × 2 ÷ 100 × (1 + 23/30) = ₹3,533.33.
Simple vs compound interest
Simple interest is charged only on the original principal. Compound interest also charges interest on interest already added. ₹1,00,000 at 10% for 2 years earns ₹20,000 simple interest, but ₹21,000 compounded yearly and about ₹21,840 compounded quarterly. For long periods the gap grows quickly; use the compound interest calculator for deposits and investments.
FAQ
How do I calculate simple interest?
Multiply principal × rate × time in years and divide by 100. ₹1,00,000 at 10% for 2 years is 1,00,000 × 10 × 2 ÷ 100 = ₹20,000, so the total amount is ₹1,20,000.
How do I calculate simple interest per month?
Monthly interest = P × R ÷ 100 ÷ 12 for a yearly rate. ₹1,00,000 at 12% a year is ₹1,000 a month. For a sekda (₹ per ₹100 per month) rate it is P × rate ÷ 100, so ₹1,00,000 at ₹2 sekda is ₹2,000 a month.
What is ₹2 interest (2 rupees byaj) in percent?
₹2 per ₹100 per month is 2% a month, which equals 24% a year in simple interest. ₹1 sekda is 12% a year, ₹1.5 is 18% and ₹3 is 36%.
How do I calculate interest between two dates?
Count the days between the dates and use T = days ÷ 365 (or ÷ 360 if your lender uses a 360-day year). For byaj-style loans, count whole months and leftover days ÷ 30. Choose "Between two dates" above and pick the day-count method.
How is interest calculated when a loan is repaid in parts?
Interest runs on the outstanding principal from one entry to the next. A part payment usually clears interest due first and then reduces the principal, so later interest is lower. The loan ledger above does this for any number of loans and repayments.
Is my data uploaded anywhere?
No. Everything runs in your browser. Ledger entries are kept only in this browser's local storage and are never sent to ITCOH.