On a sekda loan, one day's byaj is a month's byaj ÷ 30: amount × sekda ÷ 100 ÷ 30. ₹1,00,000 at ₹2 sekda is ₹66.67 a day, so 15 days is ₹1,000. Banks divide a year's interest by 365 instead: ₹65.75 a day at 24% a year. Enter the days to see all three ways.
How to calculate interest per day
Byaj for N days = Amount × Sekda × N ÷ 3,000
The same as amount × sekda ÷ 100 ÷ 30 × N: a bahi counts one day as 1/30 of a month.
With a yearly % rate, a bank counts actual days over a 365-day year:
Byaj for N days = Amount × Yearly rate × N ÷ 36,500
Three ways to count a day
| Way of counting | 1 day | 30 days | Used for |
|---|---|---|---|
| Bahi: 1/30 of a month | ₹66.67 | ₹2,000 | Sekda loans, bahi khata, shop udhar |
| Actual days ÷ 365 | ₹65.75 | ₹1,972.60 | Banks and finance companies |
| Days ÷ 360 | ₹66.67 | ₹2,000 | Only if an agreement says so |
Bahi and ÷ 360 always match for a number of days, because a month ÷ 30 is a year ÷ 360. They part ways over real dates. 1 Jan to 1 Aug 2026 is 7 months, which the bahi charges as ₹14,000. It is also 212 actual days: ₹14,133.33 at ÷ 360 and ₹13,939.73 at ÷ 365.
- Sekda loans, bahi accounts and shop udhar: the bahi way, a day as 1/30 of a month.
- Matching a bank or finance company: actual days ÷ 365. Indian banks usually count actual days over a 365-day year, the method the Indian Banks' Association set for bank deposits.
- ÷ 360: only when a written agreement says so.
Byaj for 1, 7, 10, 15, 30 and 90 days
| Days | Bahi (1/30 of a month) | Bank (÷ 365) |
|---|---|---|
| 1 | ₹66.67 | ₹65.75 |
| 7 | ₹466.67 | ₹460.27 |
| 10 | ₹666.67 | ₹657.53 |
| 15 | ₹1,000 | ₹986.30 |
| 30 | ₹2,000 | ₹1,972.60 |
| 45 | ₹3,000 | ₹2,958.90 |
| 60 | ₹4,000 | ₹3,945.21 |
| 90 | ₹6,000 | ₹5,917.81 |
For another amount, scale it: ₹50,000 is half, so 15 days at ₹2 sekda is ₹500. For whole months at any amount and rate, see the byaj chart.
Know the dates? Count months and days
A count of days suits short periods, or an agreement that counts days. When money is lent from one date to another, a bahi counts whole calendar months first and only the leftover days at 1/30. 15 Jan to 10 Mar 2026 is 1 month 23 days: ₹3,533.33 on ₹1,00,000 at ₹2 sekda, not the ₹3,600 that 54 separate days would give. The byaj calculator does this count for any two dates.
Try it in the calculator₹1,00,000 at ₹2 sekda, 15 Jan to 10 Mar, in months and days6 short answersInterest per day: quick answers
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What is the formula for interest per day?
For a sekda rate: amount × sekda ÷ 100 ÷ 30, because a bahi counts a day as 1/30 of a month. For a yearly rate a bank uses amount × rate ÷ 100 ÷ 365. ₹1,00,000 at ₹2 sekda is ₹66.67 a day; at 24% a year ÷ 365 it is ₹65.75. For several days, multiply by the days before you round.
How much is the byaj for 15 days?
Half a month's byaj, the bahi way: ₹1,00,000 at ₹2 sekda earns ₹1,000 in 15 days, and ₹50,000 earns ₹500. A bank at 24% a year counting ÷ 365 would charge ₹986.30 on ₹1,00,000. Type your amount and 15 days above to see yours.
How do I calculate interest for 30 days?
In a bahi, 30 days is one month's byaj: ₹1,00,000 at ₹2 sekda is ₹2,000. A bank counting actual days ÷ 365 charges a little less, ₹1,972.60 at 24% a year, because 30 days is less than a twelfth of 365. With dates, a 31-day calendar month still counts as one whole month in a bahi.
Why is ÷ 365 less than the bahi’s 1/30 of a month?
A bank's year has 365 days, but twelve bahi months make only 360 day-units (12 × 30). The same yearly byaj spread over more days gives a smaller day: ₹65.75 against ₹66.67 on ₹1,00,000 at 24% a year. Over a 365-day year both come to ₹24,000.
What if I know the dates, not the number of days?
Use the byaj calculator. It counts whole calendar months first and only the leftover days at 1/30, as a bahi does. 15 Jan to 10 Mar 2026 is 1 month 23 days: ₹3,533.33 on ₹1,00,000 at ₹2 sekda, not the ₹3,600 that 54 separate days would give.
Can I work out byaj for days at a yearly % rate?
Yes. Switch the rate to % a year. The bahi way then takes a day as the year ÷ 360 (a month ÷ 30), and the bank way as the year ÷ 365. ₹2,00,000 at 18% a year for 45 days is ₹4,500 the bahi way and ₹4,438.36 at ÷ 365.
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