₹2 means 2% a month
On ₹1,00,000, interest of ₹2 per ₹100 a month, for 1 month
- Time1 month
- Interest amount₹1,00,000 × 2 ÷ 100 × 1₹2,000
- If ₹2 is wrongly read as 2% a year: ₹166.67.
Interest on money you can check, line by line
Vaddi Book works out interest the way people say it in villages: ₹2 per ₹100 a month. Every answer comes with the rules used to get it. You can also keep a book of the money you gave and the money you took.
On ₹1,00,000, interest of ₹2 per ₹100 a month
from 13 Oct 2025 to 13 Oct 2026
Interest amount
₹24,000
Total with principal: ₹1,24,000
How was this counted?
- Interest for one month₹1,00,000 × 2 ÷ 100₹2,000
- Time12 months. The start day is not counted.12
- Interest for 12 months₹2,000 × 12₹24,000
The app prints a slip like this under every answer, every payment and every statement. In the app, tap any rule to see the answer under the other choice.
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In short
- No login and no account
- Your records stay on your phone
- Free. One small ad, only under the calculator answer
- Telugu first, in 11 languages
How this app calculates interest
These are the rules the app uses unless you change them. You can change each one in Settings. Whatever you choose, the slip prints the rule it used.
- Rate
- ₹ per ₹100, per month₹2 per ₹100 a month = 2% a month = 24% a year. You can also enter % a month or % a year.
- Time
- Count calendar months first. Then divide the leftover days by 30.Other choices: days ÷ 365, days ÷ 30, or 30/360.
- Start day
- Not countedFrom 1 June to 30 June is 29 days. Other choice: count both the first day and the last day.
- Month end
- 31 January to 28 February is one monthOther choice: 0 months and 28 days.
- Interest method
- Simple interestCompound interest is shown next to it. Compound interest adds the interest to the principal every 12 months, or every 6, 3 or 1 month. A leftover part period is counted as simple interest.
- Part payment
- Pays the interest due firstThe principal stays the same until all the interest due is paid. Unpaid interest does not earn interest. Other choice: add the payment to the principal.
- Rounding off the amount
- Only the final answerPaise are kept during the calculation. The answer is rounded to the rupee, and the slip also prints the exact figure.
Worked examples
Each example comes from an app review or a textbook. The last line shows what a different rule gives.
Months, not days
On ₹20,000, interest of ₹2.50 per ₹100 a month, from 22 May 2022 to 22 Jan 2024
- Time20 months
- Interest amount₹20,000 × 2.5 ÷ 100 × 20₹10,000
- If the app counts days ÷ 30 instead (610 days): ₹10,166.67.
Is the start day counted?
₹31,600 at 5% a year, from 16 Apr 2019 to 8 Sept 2019
Settings used here: % a year, and days ÷ 365.
- Time145 days. The start day is not counted.
- Interest amount₹31,600 × 5% × 145 ÷ 365₹627.67
- If both the first and the last day are counted (146 days): ₹632.00. This is the answer printed in the textbook.
A part payment goes to interest first
₹10,000 at ₹2 per ₹100 a month from 21 May 2022. ₹2,000 was paid on 21 Nov 2024. What is the balance on 21 May 2025?
- Interest for 36 months₹10,000 × 2 ÷ 100 × 36₹7,200
- Paid− ₹2,000
- Interest still due₹5,200
- Principal amount₹10,000
- Balance amount₹15,200
- If the payment is added to the principal instead: ₹15,680.
Your records
Your book stays on your phone. Save a backup file whenever you like, and the app shows the date of your last backup. Android can also back up the book to your Google account.
Read the privacy policyWhat Vaddi Book does not do
Vaddi Book does not give, take or move money. It is a calculator and a personal record book. It is not a bank, and it is not linked to any bank or government body.
Read the important notice