support simple daily interest

README.md

@@ -185,7 +185,9 @@ interest transaction on the 28th of the month, set the account note to
 By default, interest is calculated using the 30/360 method where interest is
 computed monthly using 30/360 (or 1/12) of the interest rate.  If you need to
 compute interest using the ACTUAL/ACTUAL method, set `interest:actual` in the
-note.  If you need to compute interest daily, set `interest:daily`.
+note.  If you need to compute interest daily, set `interest:daily`.  For most
+student loans, you probably want simple dailiy interest
+`interest:daily-simple`.
 
 You can optionally change the payee used for the interest transactions by
 setting `INTEREST_PAYEE_NAME` in the `.env` file.

apply-interest.js

@@ -49,6 +49,7 @@ function daysInYear(year) {
         let numPeriods = 1
         switch (kind) {
           case 'daily':
+          case 'daily-simple':
             period = daysInYear(interestTransactionDate.getFullYear());
             numPeriods = daysPassed;
             break;
@@ -60,7 +61,12 @@ function daysInYear(year) {
         }
 
         const balance = await getAccountBalance(account, interestTransactionDate);
-        const compoundedInterest = Math.round(balance * (Math.pow(1 + interestRate / period, numPeriods) - 1));
+
+        let compoundedInterest;
+        if (kind == 'daily-simple')
+            compoundedInterest = Math.round(balance * (interestRate / 365) * numPeriods);
+        else
+            compoundedInterest = Math.round(balance * (Math.pow(1 + interestRate / period, numPeriods) - 1));
 
         interestRate = showPercent(interestRate);