Daily Interest Calculator: Calculate Daily Interest Between Dates Or For A Specified Number Of Days

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Easily calculate daily interest between dates or for a number of days, either for a single loan period, or for creating a schedule of loan periods.

The daily interest loan calculator on this page will help you to quickly calculate either simple or compounding interest for a specified period of time.

You can either calculate daily interest for a single loan period, or you can create a loan schedule made up of multiple periods, each with their own time-frames, principal adjustments, and interest rates.

Plus, you can print out a copy of the running balance schedule so you can just start from where you left off on your next visit.

All these features make the calculator ideal for tracking personal loan interest, promissory note interest, or other types of owner-financed, interest bearing notes.

And finally, in case you're wondering how this calculator came into being, it was born out of the following email I received:

I need a simple interest, daily accumulated interest to do a running balance due including principal. Spreadsheet?

Example, I loan a customer $13,000.00 on a note, 10% annual (360 day) simple interest. The loan is usually secured, sometimes not. Generally these are 6 month notes but due dates are not important. No regular payments, monthly or otherwise.

Here is what and where I need help on.

At some point in time my borrower may send me a payment of $9,050.00 which is applied to the note and then 2 months later borrows $2,750.00, increasing the note. Then the next month, the borrower sends me $500.00 for the next three months running to be applied to the note.

I love getting those kinds of emails! They get my wheels turning and allow me to serve others through a work I love.

Now, if you're like me, and need to know what's going on "under the hood", here is how I set up the calculator to calculate daily interest.

How To Calculate Daily Interest

To illustrate how to calculate daily interest, I'll use the following example:

  • Principal: $10,000
  • Annual Interest Rate: 10%
  • Number of days: 90

Simple Daily Interest

To calculate the daily simple interest on a $10,000, 10% note for 90 days (please allow for rounding differences):

  1. Convert the percentage rate to a decimal: 10 ÷ 100 = 0.10
  2. Convert the annual rate to a daily rate: 0.10 ÷ 365 = 0.00027397
  3. Multiply the daily rate by the principal: 10000 × 0.00027397 = $2.74
  4. Multiply the daily interest by the number of days: $2.74 × 90 = $246.60

Since we're calculating simple interest, the $246.60 is not added to the principle for any subsequent periods.

Compounding Daily Interest

To calculate the daily compounding interest on a $10,000, 10% note for 90 days (please allow for rounding differences):

  1. Convert the percentage rate to a decimal: 10 ÷ 100 = 0.10
  2. Convert the annual rate to a daily rate: 0.10 ÷ 365 = 0.00027397
  3. Add 1 to the daily rate: 1 + 0.00027397 = 1.00027397
  4. Raise the daily rate factor to the number of days: 1.0002739790 = 1.0249538
  5. Subtract 1 from the raised factor: 1.0249538 - 1 = 0.0249538
  6. Multiply the principal by the 90-day rate factor: 10000 × 0.0249538 = $249.54

Since we're calculating compound interest, the $249.54 is added to the principal for the next compounding period.

With that, let's use the daily interest calculator to calculate simple or compounding interest for one or more loan time-frames.

Daily Interest Calculator
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Instructions: Enter the loan name (optional), starting amount, starting annual interest rate, and starting date. Then select either Simple or Compounding interest, and either 360, 364, or 365 for the days in the year.

Next, if a principal adjustment occurred (payment or additional funds borrowed), select either Decrease or Increase and enter the corresponding amount.

Next, enter the period's ending date or specify the number of days since the start (or last period) date, and then click the Calculate Daily Interest button.

If you are creating a schedule of periods to track the note's running balance, click the Add Period To Loan History button and repeat the period entry process for each interest period you wish to add (be sure to add periods in chronological order, from first to last).

Finally, click the Printer Friendly Report button to print out the running balance schedule so you can start from where you left off on your next visit.

Mouse over the blue question marks for a further explanation of each entry field. More in-depth explanations can be found in the glossary of terms located beneath the Daily Interest Calculator.

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Help Loan Start Values and Preferences
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Help Daily interest method:
Help Days in year:
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Help This period end date:
Help Number of days:
Help Period rate (if different from start rate):
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Help Period principal & interest ending balance:
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Principal: The dollar amount you are borrowing, or have borrowed.

Loan Start Values and Preferences section: Note that you can change these starting variables and preferences at any time, as the changes will automatically recalculate the loan schedule.

Starting amount: Enter the beginning loan amount.

Starting annual interest rate: Enter the starting annual interest rate expressed as a percentage (for .06, enter 6).

Start date: Select the month and day, and enter the 4-digit year of the date this loan will start accruing interest charges.

Daily interest method: Select either Simple Interest or Compounding Interest. Simple Interest will not add period interest to the principal, whereas Compounding Interest will add the daily interest charge to the principal on a daily and period basis.

Days in year: Select the number of days per year you would like the calculator to use for converting the annual interest rate to a daily interest rate.

Period Interest Calculator section: To calculate the interest for the period, be sure you have entered the starting amount, rate, and date (including the 4-digit year) in the top section, then complete the required fields (ending 4-digit year and number of days in period) in this section, then click the Calculate Daily Interest button.

If you will be entering more than one interest period, be sure to enter all periods in the order they occurred, from first to last.

Optional adjustment amount: If the borrower made a payment on the loan, select Decrease from the dropdown menu and enter the amount of the payment. If you loaned the borrower additional funds or you need to assess a late penalty, select Increase from the dropdown menu and enter the amount to increase the principal by. Otherwise, if no loan adjustments occurred in the period, leave the field blank.

This period end date: Select the month and day, and enter the 4-digit year of the date this loan period ended.

Number of days: If you entered a date in the previous line, the number of days in this interest period will be calculated for you. Otherwise, you can enter a number of days in this field and the calculator will update the month, day, and year in the previous line for you.

Period rate: If the rate charged for this interest period is different from the starting rate, enter the new rate on this line. Otherwise, if you leave the field blank, the calculator will use the starting rate for this period. Note that this field will be disabled for the first loan period.

Calculate Daily Interest button: Click this button to calculate the period interest amount, ending payoff amount, and daily rate. Note that this button must be clicked before you can add the period results to the schedule.

Period interest result: This is the amount of the interest that has accrued between the starting date (or the last entered period date) and the ending date of this period.

Period principal & interest ending balance: This is the loan payoff amount (principal plus accrued interest) as of the ending date of this period.

Daily interest rate: This is the daily interest rate being applied for this period.

Add Period To Loan History button: If you are tracking the running balance of a loan, clicking this button will add this period to the bottom of the loan schedule. Note that you must first calculate the daily interest before you will be able to add the period to the schedule.

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