Use daily interest accrual for HELOC and auto loan amortization

Mortgages and personal loans use monthly compounding (rate/12), but
HELOCs and auto loans accrue interest daily (rate/365 * actual days).
Select the calculation method based on account type and update the
disclaimer to reflect which method is being used.

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 based on standard monthly compounding. Actual values may differ slightly due to your lender's rounding practices.
+        Amounts shown are estimates using {{ isDailyAccrualAccount ? 'daily interest accrual' : 'standard monthly compounding' }}. Actual values may differ slightly due to your lender's rounding practices.
       </v-alert>
 
       <!-- Amortization Schedule -->
@@ -268,12 +268,18 @@ const snackbar = ref(false)
 const snackbarText = ref('')
 const snackbarColor = ref('success')
 
-const loanAccountTypes = ['AutoLoan', 'PersonalLoan', 'Mortgage']
+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);
+        var entries = GenerateAmortizationSchedule(loanDetail, account.Type);
         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);
+        var entries = GenerateAmortizationSchedule(l, account.Type);
         foreach (var entry in entries)
         {
             entry.LoanDetailId = l.Id;
@@ -118,11 +118,14 @@ 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;
@@ -139,12 +142,15 @@ public class LoanService : ILoanService
             paymentNum++;
             var paymentDate = startDate.AddMonths(paymentNum);
 
-            var interest = Math.Round(balance * monthlyRate, 2);
+            var interest = useDailyAccrual
+                ? 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),
@@ -181,21 +187,30 @@ public class LoanService : ILoanService
         return new LoanDefaultsResponse(0, interestRate, termMonths, hasSyncData);
     }
 
-    private static List<AmortizationEntry> GenerateAmortizationSchedule(LoanDetail loan)
+    private static bool UseDailyAccrual(AccountType type) =>
+        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 = Math.Round(balance * monthlyRate, 2);
+            var interest = useDailyAccrual
+                ? 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
             {