Use standard monthly compounding for all loan types

Daily accrual made HELOC estimates worse due to front-loaded 31-day
months. Revert to rate/12 for all types - it's the standard amortization
method and works well for mortgages and personal loans. For HELOCs and
auto loans, differences from bank statements are typically due to
variable rates, extra payments, or daily billing conventions that a
fixed amortization schedule cannot capture.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/loans/LoansView.vue

@@ -104,7 +104,7 @@
       </v-card>
 
       <v-alert v-if="loanDetail" type="info" variant="tonal" density="compact" class="mb-4">
-        Amounts shown are estimates using {{ isDailyAccrualAccount ? 'daily interest accrual' : 'standard monthly compounding' }}. Actual values may differ slightly due to your lender's rounding practices.
+        Amounts shown are estimates based on standard monthly compounding. Actual values may differ due to your lender's rounding practices, extra payments, or rate changes.
       </v-alert>
 
       <!-- Amortization Schedule -->
@@ -269,17 +269,10 @@ const snackbarText = ref('')
 const snackbarColor = ref('success')
 
 const loanAccountTypes = ['AutoLoan', 'PersonalLoan', 'Mortgage', 'LineOfCredit']
-const dailyAccrualTypes = ['AutoLoan', 'LineOfCredit']
-
 const loanAccounts = computed(() =>
   accountsStore.accounts.filter(a => a.hasLoanDetail || loanAccountTypes.includes(a.type))
 )
 
-const isDailyAccrualAccount = computed(() => {
-  const account = accountsStore.accounts.find(a => a.id === props.id)
-  return account ? dailyAccrualTypes.includes(account.type) : false
-})
-
 const amortHeaders = [
   { title: '#', key: 'paymentNumber', width: '60px' },
   { title: 'Date', key: 'paymentDate', width: '110px' },

src/Purrse.Api/Services/LoanService.cs

@@ -49,7 +49,7 @@ public class LoanService : ILoanService
             ExtraPayment = request.ExtraPayment
         };
 
-        var entries = GenerateAmortizationSchedule(loanDetail, account.Type);
+        var entries = GenerateAmortizationSchedule(loanDetail);
         loanDetail.AmortizationEntries = entries;
 
         _db.LoanDetails.Add(loanDetail);
@@ -82,7 +82,7 @@ public class LoanService : ILoanService
         l.EscrowAmount = request.EscrowAmount;
         l.ExtraPayment = request.ExtraPayment;
 
-        var entries = GenerateAmortizationSchedule(l, account.Type);
+        var entries = GenerateAmortizationSchedule(l);
         foreach (var entry in entries)
         {
             entry.LoanDetailId = l.Id;
@@ -118,14 +118,11 @@ public class LoanService : ILoanService
 
         // Build new schedule with extra payments
         var balance = Math.Abs(account.Balance);
-        var useDailyAccrual = UseDailyAccrual(account.Type);
         var monthlyRate = l.InterestRate / 100m / 12m;
-        var dailyRate = l.InterestRate / 100m / 365m;
         var extraMonthly = request.ExtraMonthlyPayment ?? 0;
         var basePayment = l.MonthlyPayment - (l.EscrowAmount ?? 0);
         var now = DateTime.UtcNow;
         var startDate = new DateTime(now.Year, now.Month, l.OriginationDate.Day, 0, 0, 0, DateTimeKind.Utc);
-        var previousDate = startDate;
 
         var newEntries = new List<AmortizationEntryResponse>();
         int paymentNum = 0;
@@ -142,15 +139,12 @@ public class LoanService : ILoanService
             paymentNum++;
             var paymentDate = startDate.AddMonths(paymentNum);
 
-            var interest = useDailyAccrual
+            var interest = Math.Round(balance * monthlyRate, 2);
-                ? Math.Round(balance * dailyRate * (paymentDate - previousDate).Days, 2)
-                : Math.Round(balance * monthlyRate, 2);
             var principal = Math.Min(basePayment + extraMonthly - interest, balance);
             if (principal < 0) principal = 0;
 
             balance -= principal;
             if (balance < 0.01m) balance = 0;
-            previousDate = paymentDate;
 
             newEntries.Add(new AmortizationEntryResponse(
                 paymentNum, paymentDate, principal + interest + (l.EscrowAmount ?? 0),
@@ -187,30 +181,21 @@ public class LoanService : ILoanService
         return new LoanDefaultsResponse(0, interestRate, termMonths, hasSyncData);
     }
 
-    private static bool UseDailyAccrual(AccountType type) =>
+    private static List<AmortizationEntry> GenerateAmortizationSchedule(LoanDetail loan)
-        type is AccountType.AutoLoan or AccountType.LineOfCredit;
-
-    private static List<AmortizationEntry> GenerateAmortizationSchedule(LoanDetail loan, AccountType accountType)
     {
         var entries = new List<AmortizationEntry>();
         var balance = loan.OriginalBalance;
-        var useDailyAccrual = UseDailyAccrual(accountType);
         var monthlyRate = loan.InterestRate / 100m / 12m;
-        var dailyRate = loan.InterestRate / 100m / 365m;
         var payment = loan.MonthlyPayment - (loan.EscrowAmount ?? 0);
         var extra = loan.ExtraPayment ?? 0;
-        var previousDate = loan.OriginationDate.AddMonths(-1);
 
         for (int i = 1; i <= loan.TermMonths && balance > 0; i++)
         {
             var paymentDate = loan.OriginationDate.AddMonths(i - 1);
-            var interest = useDailyAccrual
+            var interest = Math.Round(balance * monthlyRate, 2);
-                ? Math.Round(balance * dailyRate * (paymentDate - previousDate).Days, 2)
-                : Math.Round(balance * monthlyRate, 2);
             var principal = Math.Min(payment + extra - interest, balance);
             balance -= principal;
             if (balance < 0.01m) balance = 0;
-            previousDate = paymentDate;
 
             entries.Add(new AmortizationEntry
             {