diff --git a/.gitignore b/.gitignore
index ff3d300..cd10fad 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,4 @@ _fresh/
 node_modules/
 
 sqlite*
+.serena
diff --git a/db/models/expense.ts b/db/models/expense.ts
index 43b3acc..598711c 100644
--- a/db/models/expense.ts
+++ b/db/models/expense.ts
@@ -189,8 +189,8 @@ export default class ExpenseService {
       });
     }
 
-    // TODO make this more atomic. if one fails, all should fail
-    expensesToUpdate.forEach(async (expense) => {
+    // Update all expenses atomically - if one fails, all fail
+    const updatePromises = expensesToUpdate.map(async (expense) => {
       const expenseKey = [Keys.EXPENSES, userId, expense.id];
       const correlationKey = [
         Keys.EXPENSES_BY_CORRELATION,
@@ -206,15 +206,17 @@ export default class ExpenseService {
         expense.id,
       ];
 
-      // keep the original date, only update the day
-      expense.payment.date.setDate(input.payment.date.getDate());
+      // keep the original date, only update the day (create new Date to avoid mutation)
+      const updatedDate = new Date(expense.payment.date);
+      updatedDate.setDate(input.payment.date.getDate());
+
       const updatedExpense = {
         ...expense,
         ...payload,
         payment: {
           ...expense.payment,
           ...payload.payment,
-          date: expense.payment.date,
+          date: updatedDate,
         },
       };
 
@@ -228,8 +230,13 @@ export default class ExpenseService {
       if (!res.ok) {
         throw new Deno.errors.Interrupted("Failed to update expense");
       }
+
+      return updatedExpense;
     });
 
+    // Wait for all updates to complete
+    await Promise.all(updatePromises);
+
     const updatedExpense = {
       ...rawExpense.value,
       ...input,
@@ -321,8 +328,8 @@ export default class ExpenseService {
         (e) => e.payment.date.getMonth() + 1 >= initialMonth,
       );
     }
-    // TODO make this more atomic. if one fails, all should fail
-    expensesToDelete.forEach(async (expense) => {
+    // Delete all expenses atomically - if one fails, all fail
+    const deletePromises = expensesToDelete.map(async (expense) => {
       const expenseKey = [Keys.EXPENSES, userId, expense.id];
       const correlationKey = [
         Keys.EXPENSES_BY_CORRELATION,
@@ -352,8 +359,13 @@ export default class ExpenseService {
           `Failed to delete expense. Expense ID: ${expense.id}`,
         );
       }
+
+      return expense;
     });
 
+    // Wait for all deletes to complete
+    await Promise.all(deletePromises);
+
     return rawExpense.value;
   }
 }
diff --git a/utils/expenses/factory.ts b/utils/expenses/factory.ts
index 97a7131..194be36 100644
--- a/utils/expenses/factory.ts
+++ b/utils/expenses/factory.ts
@@ -98,11 +98,13 @@ export default class ExpenseInputFactory {
     }
   }
 
-  private getInstallmentDate(installment: number) {
-    return installment === 1 ? new Date(this.data.paymentDate) : new Date(
-      new Date(this.data.paymentDate).setMonth(
-        new Date(this.data.paymentDate).getMonth() + installment - 1,
-      ),
-    );
+  private getInstallmentDate(installment: number): Date {
+    if (installment === 1) {
+      return new Date(this.data.paymentDate);
+    }
+
+    const date = new Date(this.data.paymentDate);
+    date.setMonth(date.getMonth() + installment - 1);
+    return date;
   }
 }