From 428e18bb41d556f6046a1d7855f1d1fb2d746931 Mon Sep 17 00:00:00 2001
From: Catherine Renelle <32781029+catrenelle@users.noreply.github.com>
Date: Sat, 14 Feb 2026 17:26:55 -0500
Subject: [PATCH] Fix date display timezone shift and revert to standard
 monthly interest

formatDate was parsing UTC timestamps in local time, shifting dates
back a day in western timezones. Strip the time portion before parsing
so dates display correctly.

Revert interest calculation from daily accrual back to standard monthly
compounding (rate/12) with per-payment rounding. This matches how
mortgage servicers calculate interest and produces correct amortization
schedules.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 frontend/src/utils/formatters.ts       |  2 +-
 src/Purrse.Api/Services/LoanService.cs | 14 ++++----------
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/frontend/src/utils/formatters.ts b/frontend/src/utils/formatters.ts
index 995e23b..a22e9d2 100644
--- a/frontend/src/utils/formatters.ts
+++ b/frontend/src/utils/formatters.ts
@@ -5,7 +5,7 @@ export function formatCurrency(amount: number): string {
 }
 
 export function formatDate(date: string): string {
-  return format(parseISO(date), 'MM/dd/yyyy')
+  return format(parseISO(date.split('T')[0]), 'MM/dd/yyyy')
 }
 
 export function formatDateTime(date: string): string {
diff --git a/src/Purrse.Api/Services/LoanService.cs b/src/Purrse.Api/Services/LoanService.cs
index 149713b..071326e 100644
--- a/src/Purrse.Api/Services/LoanService.cs
+++ b/src/Purrse.Api/Services/LoanService.cs
@@ -118,12 +118,11 @@ public class LoanService : ILoanService
 
         // Build new schedule with extra payments
         var balance = Math.Abs(account.Balance);
-        var dailyRate = l.InterestRate / 100m / 365m;
+        var monthlyRate = l.InterestRate / 100m / 12m;
         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;
@@ -139,15 +138,13 @@ public class LoanService : ILoanService
         {
             paymentNum++;
             var paymentDate = startDate.AddMonths(paymentNum);
-            var days = (paymentDate - previousDate).Days;
 
-            var interest = balance * dailyRate * days;
+            var interest = 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),
@@ -188,20 +185,17 @@ public class LoanService : ILoanService
     {
         var entries = new List<AmortizationEntry>();
         var balance = loan.OriginalBalance;
-        var dailyRate = loan.InterestRate / 100m / 365m;
+        var monthlyRate = loan.InterestRate / 100m / 12m;
         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 days = (paymentDate - previousDate).Days;
-            var interest = balance * dailyRate * days;
+            var interest = 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
             {