feat: Add selectable currency (AUD/USD/EUR/etc) with dropdown

backend/src/db/mod.rs

@@ -39,6 +39,11 @@ pub async fn run_migrations(pool: &SqlitePool) -> Result<(), sqlx::Error> {
         .await
         .ok();
 
+    sqlx::query("ALTER TABLE users ADD COLUMN currency TEXT NOT NULL DEFAULT 'USD'")
+        .execute(pool)
+        .await
+        .ok();
+
     sqlx::query("UPDATE users SET retirement_savings = roth_ira WHERE retirement_savings = 0 AND roth_ira IS NOT NULL AND roth_ira > 0")
         .execute(pool)
         .await

backend/src/handlers/auth.rs

@@ -14,6 +14,7 @@ use validator::Validate;
 
 use crate::error::PaymeError;
 use crate::middleware::auth::Claims;
+use crate::models::User;
 
 #[derive(Deserialize, ToSchema, Validate)]
 pub struct AuthRequest {
@@ -157,7 +158,7 @@ pub async fn logout(jar: CookieJar) -> impl IntoResponse {
     get,
     path = "/api/auth/me",
     responses(
-        (status = 200, description = "Current user retrieved", body = AuthResponse),
+        (status = 200, description = "Current user retrieved", body = crate::models::User),
         (status = 404, description = "User not found"),
         (status = 500, description = "Internal server error")
     ),
@@ -168,17 +169,16 @@ pub async fn logout(jar: CookieJar) -> impl IntoResponse {
 pub async fn me(
     State(pool): State<SqlitePool>,
     axum::Extension(claims): axum::Extension<Claims>,
-) -> Result<Json<AuthResponse>, PaymeError> {
-    let user: (i64, String) = sqlx::query_as("SELECT id, username FROM users WHERE id = ?")
-        .bind(claims.sub)
-        .fetch_optional(&pool)
-        .await?
-        .ok_or(PaymeError::NotFound)?;
+) -> Result<Json<crate::models::User>, PaymeError> {
+    let user = sqlx::query_as::<_, crate::models::User>(
+        "SELECT id, username, savings, savings_goal, retirement_savings, currency FROM users WHERE id = ?"
+    )
+    .bind(claims.sub)
+    .fetch_optional(&pool)
+    .await?
+    .ok_or(PaymeError::NotFound)?;
 
-    Ok(Json(AuthResponse {
-        id: user.0,
-        username: user.1,
-    }))
+    Ok(Json(user))
 }
 
 pub async fn export_db(
@@ -359,3 +359,75 @@ pub async fn clear_all_data(
         Json(serde_json::json!({"message": "All data cleared"})),
     ))
 }
+
+#[derive(Deserialize, ToSchema)]
+pub struct CurrencyRequest {
+    pub currency: String,
+}
+
+#[utoipa::path(
+    put,
+    path = "/api/auth/currency",
+    request_body = CurrencyRequest,
+    responses(
+        (status = 200, description = "Currency updated successfully", body = crate::models::User),
+        (status = 400, description = "Invalid currency"),
+        (status = 500, description = "Internal server error")
+    ),
+    tag = "Auth",
+    summary = "Update user currency",
+    description = "Updates the authenticated user's preferred currency."
+)]
+pub async fn update_currency(
+    State(pool): State<SqlitePool>,
+    axum::Extension(claims): axum::Extension<Claims>,
+    Json(payload): Json<CurrencyRequest>,
+) -> Result<Json<crate::models::User>, PaymeError> {
+    let currency = payload.currency.to_uppercase();
+
+    // Validate currency code (basic validation for common currencies)
+    let valid_currencies = vec!["USD", "EUR", "GBP", "JPY", "CAD", "AUD", "CHF", "CNY", "INR", "MXN", "BRL", "ZAR"];
+    if !valid_currencies.contains(&currency.as_str()) {
+        return Err(PaymeError::BadRequest(format!("Unsupported currency: {}", currency)));
+    }
+
+    sqlx::query("UPDATE users SET currency = ? WHERE id = ?")
+        .bind(&currency)
+        .bind(claims.sub)
+        .execute(&pool)
+        .await?;
+
+    let user = sqlx::query_as::<_, crate::models::User>(
+        "SELECT id, username, savings, savings_goal, retirement_savings, currency FROM users WHERE id = ?"
+    )
+    .bind(claims.sub)
+    .fetch_one(&pool)
+    .await?;
+
+    Ok(Json(user))
+}
+
+#[utoipa::path(
+    get,
+    path = "/api/auth/currency",
+    responses(
+        (status = 200, description = "User currency retrieved", body = crate::models::User),
+        (status = 500, description = "Internal server error")
+    ),
+    tag = "Auth",
+    summary = "Get user currency",
+    description = "Retrieves the authenticated user's preferred currency."
+)]
+pub async fn get_currency(
+    State(pool): State<SqlitePool>,
+    axum::Extension(claims): axum::Extension<Claims>,
+) -> Result<Json<crate::models::User>, PaymeError> {
+    let user = sqlx::query_as::<_, crate::models::User>(
+        "SELECT id, username, savings, savings_goal, retirement_savings, currency FROM users WHERE id = ?"
+    )
+    .bind(claims.sub)
+    .fetch_one(&pool)
+    .await?;
+
+    Ok(Json(user))
+}

backend/src/lib.rs

@@ -32,6 +32,8 @@ pub fn create_app(pool: SqlitePool) -> Router {
         .route("/api/auth/me", get(auth::me))
         .route("/api/auth/change-username", put(auth::change_username))
         .route("/api/auth/change-password", put(auth::change_password))
+        .route("/api/auth/currency", get(auth::get_currency))
+        .route("/api/auth/currency", put(auth::update_currency))
         .route("/api/auth/clear-data", delete(auth::clear_all_data))
         .route("/api/export", get(auth::export_db))
         .route("/api/months", get(months::list_months))

backend/src/models/mod.rs

@@ -2,6 +2,16 @@ use chrono::{DateTime, NaiveDate, Utc};
 use serde::{Deserialize, Serialize};
 use utoipa::ToSchema;
 
+#[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow, ToSchema)]
+pub struct User {
+    pub id: i64,
+    pub username: String,
+    pub savings: f64,
+    pub savings_goal: f64,
+    pub retirement_savings: f64,
+    pub currency: String,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow, ToSchema)]
 pub struct FixedExpense {
     pub id: i64,

backend/tests/common/mod.rs

@@ -41,6 +41,7 @@ async fn run_migrations(pool: &SqlitePool) {
             savings REAL NOT NULL DEFAULT 0,
             savings_goal REAL NOT NULL DEFAULT 0,
             retirement_savings REAL NOT NULL DEFAULT 0,
+            currency TEXT NOT NULL DEFAULT 'USD',
             created_at TEXT NOT NULL DEFAULT (datetime('now'))
         )
         "#,

frontend/src/api/client.ts

@@ -37,9 +37,9 @@ export const api = {
         body: JSON.stringify({ username, password }),
       }),
     logout: () => request<void>("/auth/logout", { method: "POST" }),
-    me: () => request<{ id: number; username: string }>("/auth/me"),
+    me: () => request<User>("/auth/me"),
     changeUsername: (newUsername: string) =>
-      request<{ id: number; username: string }>("/auth/change-username", {
+      request<User>("/auth/change-username", {
         method: "PUT",
         body: JSON.stringify({ new_username: newUsername }),
       }),
@@ -48,6 +48,12 @@ export const api = {
         method: "PUT",
         body: JSON.stringify({ current_password: currentPassword, new_password: newPassword }),
       }),
+    getCurrency: () => request<User>("/auth/currency"),
+    updateCurrency: (currency: string) =>
+      request<User>("/auth/currency", {
+        method: "PUT",
+        body: JSON.stringify({ currency }),
+      }),
     clearAllData: (password: string) =>
       request<{ message: string }>("/auth/clear-data", {
         method: "DELETE",
@@ -219,6 +225,15 @@ export interface UserExport {
   }[];
 }
 
+export interface User {
+  id: number;
+  username: string;
+  savings: number;
+  savings_goal: number;
+  retirement_savings: number;
+  currency: string;
+}
+
 export interface Month {
   id: number;
   user_id: number;

frontend/src/components/BudgetSection.tsx

@@ -1,6 +1,8 @@
 import { useState } from "react";
 import { Plus, Trash2, Edit2, Check, X, Settings } from "lucide-react";
 import { MonthlyBudgetWithCategory, BudgetCategory, api } from "../api/client";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 import { Card } from "./ui/Card";
 import { Input } from "./ui/Input";
 import { Button } from "./ui/Button";
@@ -22,6 +24,8 @@ export function BudgetSection({
   isReadOnly,
   onUpdate,
 }: BudgetSectionProps) {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const [isManaging, setIsManaging] = useState(false);
   const [isAddingCategory, setIsAddingCategory] = useState(false);
   const [editingCategoryId, setEditingCategoryId] = useState<number | null>(null);
@@ -131,7 +135,7 @@ export function BudgetSection({
                     </span>
                     <div className="flex items-center gap-2">
                       <span className="text-xs text-charcoal-500 dark:text-charcoal-400">
-                        ${budget.spent_amount.toFixed(2)} / ${budget.allocated_amount.toFixed(2)}
+                        {formatCurrency(budget.spent_amount, currency)} / {formatCurrency(budget.allocated_amount, currency)}
                       </span>
                       {!isReadOnly && (
                         <button
@@ -198,7 +202,7 @@ export function BudgetSection({
                   <span className="text-sm">{cat.label}</span>
                   <div className="flex items-center gap-2">
                     <span className="text-xs text-charcoal-500">
-                      ${cat.default_amount.toFixed(2)}
+                      {formatCurrency(cat.default_amount, currency)}
                     </span>
                     <button
                       onClick={() => startEditCategory(cat)}

frontend/src/components/FixedExpenses.tsx

@@ -1,6 +1,8 @@
 import { useState } from "react";
 import { Plus, Trash2, Edit2, Check, X, Settings } from "lucide-react";
 import { FixedExpense, api } from "../api/client";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 import { Card } from "./ui/Card";
 import { Input } from "./ui/Input";
 import { Button } from "./ui/Button";
@@ -12,6 +14,8 @@ interface FixedExpensesProps {
 }
 
 export function FixedExpenses({ expenses, onUpdate }: FixedExpensesProps) {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const [isManaging, setIsManaging] = useState(false);
   const [isAdding, setIsAdding] = useState(false);
   const [editingId, setEditingId] = useState<number | null>(null);
@@ -81,7 +85,7 @@ export function FixedExpenses({ expenses, onUpdate }: FixedExpensesProps) {
                 {expense.label}
               </span>
               <span className="text-sm text-charcoal-600 dark:text-charcoal-400">
-                ${expense.amount.toFixed(2)}
+                {formatCurrency(expense.amount, currency)}
               </span>
             </div>
           ))}
@@ -98,7 +102,7 @@ export function FixedExpenses({ expenses, onUpdate }: FixedExpensesProps) {
               Total
             </span>
             <span className="text-sm font-semibold text-charcoal-800 dark:text-sand-100">
-              ${total.toFixed(2)}
+              {formatCurrency(total, currency)}
             </span>
           </div>
         )}
@@ -142,7 +146,7 @@ export function FixedExpenses({ expenses, onUpdate }: FixedExpensesProps) {
                 <div className="flex items-center justify-between py-2 border-b border-sand-200 dark:border-charcoal-800">
                   <span className="text-sm">{expense.label}</span>
                   <div className="flex items-center gap-2">
-                    <span className="text-sm">${expense.amount.toFixed(2)}</span>
+                    <span className="text-sm">{formatCurrency(expense.amount, currency)}</span>
                     <button
                       onClick={() => startEdit(expense)}
                       className="p-1 hover:bg-sand-200 dark:hover:bg-charcoal-800"

frontend/src/components/IncomeSection.tsx

@@ -1,6 +1,8 @@
 import { useState } from "react";
 import { Plus, Trash2, Edit2, Check, X } from "lucide-react";
 import { IncomeEntry, api } from "../api/client";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 import { Card } from "./ui/Card";
 import { Input } from "./ui/Input";
 import { Button } from "./ui/Button";
@@ -13,6 +15,8 @@ interface IncomeSectionProps {
 }
 
 export function IncomeSection({ monthId, entries, isReadOnly, onUpdate }: IncomeSectionProps) {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const [isAdding, setIsAdding] = useState(false);
   const [editingId, setEditingId] = useState<number | null>(null);
   const [label, setLabel] = useState("");
@@ -110,7 +114,7 @@ export function IncomeSection({ monthId, entries, isReadOnly, onUpdate }: Income
                 </span>
                 <div className="flex items-center gap-2">
                   <span className="text-sm font-medium text-sage-600 dark:text-sage-400">
-                    ${entry.amount.toFixed(2)}
+                    {formatCurrency(entry.amount, currency)}
                   </span>
                   {!isReadOnly && (
                     <>

frontend/src/components/ItemsSection.tsx

@@ -1,6 +1,8 @@
 import { useState } from "react";
 import { Plus, Trash2, Edit2, Check, X } from "lucide-react";
 import { ItemWithCategory, BudgetCategory, api } from "../api/client";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 import { Card } from "./ui/Card";
 import { Input } from "./ui/Input";
 import { Select } from "./ui/Select";
@@ -21,6 +23,8 @@ export function ItemsSection({
   isReadOnly,
   onUpdate,
 }: ItemsSectionProps) {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const [isAdding, setIsAdding] = useState(false);
   const [editingId, setEditingId] = useState<number | null>(null);
   const [description, setDescription] = useState("");
@@ -243,7 +247,7 @@ export function ItemsSection({
                       </span>
                     </td>
                     <td className="py-2 text-right font-medium text-terracotta-600 dark:text-terracotta-400">
-                      ${item.amount.toFixed(2)}
+                      {formatCurrency(item.amount, currency)}
                     </td>
                     {!isReadOnly && (
                       <td className="py-2">

frontend/src/components/ProjectedSavingsCard.tsx

@@ -1,5 +1,7 @@
 import { TrendingUp, HelpCircle } from "lucide-react";
 import { Card } from "./ui/Card";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 
 interface ProjectedSavingsCardProps {
   savings: number;
@@ -8,6 +10,8 @@ interface ProjectedSavingsCardProps {
 }
 
 export function ProjectedSavingsCard({ savings, remaining, onAnalyzeClick }: ProjectedSavingsCardProps) {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const projected = savings + remaining;
 
   return (
@@ -20,7 +24,7 @@ export function ProjectedSavingsCard({ savings, remaining, onAnalyzeClick }: Pro
       </div>
       <div className="flex items-center justify-between">
         <span className="text-sm font-semibold text-sage-700 dark:text-sage-400">
-          ${projected.toFixed(2)}
+          {formatCurrency(projected, currency)}
         </span>
         {onAnalyzeClick && (
           <button

frontend/src/components/RetirementSavingsCard.tsx

@@ -3,8 +3,12 @@ import { TrendingUp, Pencil, Check, X } from "lucide-react";
 import { api } from "../api/client";
 import { Card } from "./ui/Card";
 import { Input } from "./ui/Input";
+import { useAuth } from "../context/AuthContext";
+import { formatCurrency } from "../utils/currencyFormatter";
 
 export function RetirementSavingsCard() {
+  const { user } = useAuth();
+  const currency = user?.currency || "USD";
   const [amount, setAmount] = useState<number>(0);
   const [isEditing, setIsEditing] = useState(false);
   const [editValue, setEditValue] = useState("");
@@ -63,7 +67,7 @@ export function RetirementSavingsCard() {
           ) : (
             <div className="flex items-center gap-2">
               <span className="text-xl font-semibold text-sage-600 dark:text-sage-400">
-                ${amount.toFixed(2)}
+                {formatCurrency(amount, currency)}
               </span>
               <button
                 onClick={startEdit}