This tool calculates the interest rate as most banks do.
This service uses the "daily interest calculation" method where the actual number of days in the month is used
and one year is set at 365 days and in a leap year 366 days.
To calculate the interest rate the following input data are required:
 A list of amounts to and from a savings account with matching deposit or withdrawal dates.
The dates must be value dates and no posting dates.
 A list of interim interest changes with corresponding dates.
This is especially the case if you have a savings account with a variable interest rate.
 A list of dates when interest is credited to the savings account.
Example savings account with deposits and withdrawals and interest rate changes:
 On 24032007 your balance in your savings account is 10000.00 and the interest rate is 4.50%.
 balance = 10000.00
 interest days = 35
 interest numbers = 10000.00 / 100 * 35 = 3500
 interest amount = 3500 * 4.50 / 365 = 43.1507
 total accrued interest = 43.1507
 On 28042007 1000.00 is deposited.
 balance = 10000.00 + 1000.00 = 11000.00
 interest days = 58
 interest numbers = 11000.00 / 100 * 58 = 6380
 interest amount = 6380 * 4.50 / 365 = 78.6575
 total accrued interest = 43.1507 + 78.6575 = 121.8082
 On 25062007 the interest rate is changed to 4.00%.
 balance = 11000.00
 interest days = 82
 interest numbers = 11000.00 / 100 * 82 = 9020
 interest amount = 9020 * 4.00 / 365 = 98.8493
 total accrued interest = 121.8082 + 98.8493 = 220.6575
 On 15092007 2000.00 is withdrawn.
 balance = 11000.00  2000.00 = 9000.00
 interest days = 76
 interest numbers = 9000.00 / 100 * 76 = 6840
 interest amount = 6840 * 4.00 / 365 = 74.9589
 total accrued interest = 220.6575 + 74.9589 = 295.6164
 On 30112007 interest is credited to your savings account.
 interest paid on savings account = 295.6164
 balance = 9000.00 + 295.6164 = 9295.62
 interest days = 31
 interest numbers = 9295.62 / 100 * 31 = 2881.6422
 interest amount = 2881.6422 * 4.00 / 365 = 31.5796
 total accrued interest = 31.5796
 On 31122007 the interest rate remains unchanged at 4.00%.
Note: When transitioning to another year, always specify the interest rate on Dec 31.
 balance = 9295.62
 interest days = 1
 interest numbers = 9295.62 / 100 * 1 = 92.9562
 interest amount = 92.9562 * 4.00 / 365 = 1.0187
 total accrued interest = 31.5796 + 1.0187 = 32.5983
 On 112008 the interest rate remains unchanged at 4.00%.
Note: When transitioning from another year, always specify the interest rate on Jan 1.
 balance = 9295.62
 interest days = 9
 interest numbers = 9295.62 / 100 * 9 = 836.6058
 interest amount = 836.6058 * 4.00 / 366 (leap year) = 9.1432
 total accrued interest = 32.5983 + 9.1432 = 41.7415
 On 1012008 3000.00 is deposited.
 balance = 9295.62 + 3000.00 = 12295.62
 interest days = 112
 interest numbers = 12295.62 / 100 * 112 = 13771.0944
 interest amount = 13771.0944 * 4.00 / 366 = 150.5038
 total accrued interest = 41.7415 + 150.5038 = 192.2453
 On 1052008 the interest rate is changed to 3.50%.
 balance = 12295.62
 interest days = 108
 interest numbers = 12295.62 / 100 * 108 = 13279.2696
 interest amount = 13279.2696 * 3.50 / 366 (leap year) = 126.9876
 total accrued interest = 192.2453 + 126.9876 = 319.2329
 On 1782008 5000.00 is deposited.
 balance = 12295.62 + 5000.00 = 17295.62
 interest days = 105
 interest numbers = 17295.62 / 100 * 105 = 18160.4010
 interest amount = 18160.4010 * 3.50 / 366 (leap year) = 173.6650
 total accrued interest = 319.2329 + 173.6650 = 492.8979
 On 30112008 interest is credited to your savings account.
 interest paid on savings account = 492.8979
 balance = 17295.62 + 492.8979= 17788.52
 interest days = 31
 interest numbers = 17788.52 / 100 * 31 = 5514.4412
 interest amount = 5514.4412 * 3.50 / 366 (leap year) = 52.7337
 total accrued interest = 52.7337
 The final date of the calculation is 31122008.
 balance = 17788.52
 total accrued interest = 52.7337
Explanation balance:
The balance are all deposits and withdrawals added together at the relevant date.
If on the same date interest is credited to the savings account, the interest is added to the balance.
Explanation interest days:
In calculating the number of days (interest days) the first day shall be counted but not the last day.
In the example above, March 24 (step 1) is counted but the next date April 28 (step 2) is not.
The number of days (interest days) during that period is 35.
Explanation interest numbers:
Banks use interest numbers when interim interest rate changes take place and there are many deposits and withdrawals.
The interest numbers are calculated by dividing the balance by 100 and then multiplied by the number of interest days.
Explanation interest amount:
The interest amount is calculated by multiplying the interest number with the interest rate and then dividing it by 365 (in a leap year by 366).
Note: The specified date is used to determine whether it is a leap year or not.
Explanation total accrued interest and interest paid on savings account:
The total accrued interest are all interest amounts added together at the relevant date.
The interest that is credited to the savings account is the total accrued interest from the previous period (see step 5 and 10).
Once the interest is credited to the savings account, the total accrued interest is set to 0 plus current calculated interest amount.
Explanation final date:
The interest calculation starts from the first transaction date in field 1 until and including the end date you specify separately.
If you had put the end date on 30112007 in the example above, the interest calculation would start from 24032007 until and including 30112007.
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Input calculation of the interest payment:

Output calculation of the interest payment:

