diff --git a/currency_utils.py b/currency_utils.py
new file mode 100644
index 0000000..426d163
--- /dev/null
+++ b/currency_utils.py
@@ -0,0 +1,53 @@
+# Currency conversion utilities for Client Extension API boundary
+from decimal import Decimal
+from typing import Union
+
+
+def gtq_to_centavos(gtq_amount: Union[float, int, str]) -> int:
+    """Convert GTQ to centavos for database storage"""
+    return int(Decimal(str(gtq_amount)) * 100)
+
+
+def centavos_to_gtq(centavos: int) -> float:
+    """Convert centavos to GTQ for API responses"""
+    return float(centavos) / 100
+
+
+def format_gtq_currency(centavos: int) -> str:
+    """Format centavos as GTQ currency string"""
+    gtq_amount = centavos_to_gtq(centavos)
+    return f"Q{gtq_amount:.2f}"
+
+
+# Conversion helpers for client API responses
+def dashboard_summary_db_to_api(summary_db) -> dict:
+    """Convert database dashboard summary to API response"""
+    return {
+        "user_id": summary_db.user_id,
+        "total_sats_accumulated": summary_db.total_sats_accumulated,
+        "total_fiat_invested_gtq": centavos_to_gtq(summary_db.total_fiat_invested),
+        "pending_fiat_deposits_gtq": centavos_to_gtq(summary_db.pending_fiat_deposits),
+        "current_sats_fiat_value_gtq": centavos_to_gtq(int(summary_db.current_sats_fiat_value)),
+        "average_cost_basis": summary_db.average_cost_basis,
+        "current_fiat_balance_gtq": centavos_to_gtq(summary_db.current_fiat_balance),
+        "total_transactions": summary_db.total_transactions,
+        "dca_mode": summary_db.dca_mode,
+        "dca_status": summary_db.dca_status,
+        "last_transaction_date": summary_db.last_transaction_date,
+        "currency": summary_db.currency
+    }
+
+
+def transaction_db_to_api(transaction_db) -> dict:
+    """Convert database transaction to API response"""
+    return {
+        "id": transaction_db.id,
+        "amount_sats": transaction_db.amount_sats,
+        "amount_fiat_gtq": centavos_to_gtq(transaction_db.amount_fiat),
+        "exchange_rate": transaction_db.exchange_rate,
+        "transaction_type": transaction_db.transaction_type,
+        "status": transaction_db.status,
+        "created_at": transaction_db.created_at,
+        "transaction_time": transaction_db.transaction_time,
+        "lamassu_transaction_id": transaction_db.lamassu_transaction_id
+    }
\ No newline at end of file
diff --git a/models.py b/models.py
index 267d22f..cdcb10f 100644
--- a/models.py
+++ b/models.py
@@ -6,9 +6,39 @@ from typing import List, Optional
 from pydantic import BaseModel
 
 
-# Client Dashboard Data Models
+# API Models for Client Dashboard (Frontend communication in GTQ)
+class ClientDashboardSummaryAPI(BaseModel):
+    """API model - client dashboard summary in GTQ"""
+    user_id: str
+    total_sats_accumulated: int
+    total_fiat_invested_gtq: float  # Confirmed deposits in GTQ
+    pending_fiat_deposits_gtq: float  # Pending deposits in GTQ
+    current_sats_fiat_value_gtq: float  # Current fiat value of total sats in GTQ
+    average_cost_basis: float  # Average sats per GTQ
+    current_fiat_balance_gtq: float  # Available balance for DCA in GTQ
+    total_transactions: int
+    dca_mode: str  # 'flow' or 'fixed'
+    dca_status: str  # 'active' or 'inactive'
+    last_transaction_date: Optional[datetime]
+    currency: str = "GTQ"
+
+
+class ClientTransactionAPI(BaseModel):
+    """API model - client transaction in GTQ"""
+    id: str
+    amount_sats: int
+    amount_fiat_gtq: float  # Amount in GTQ
+    exchange_rate: float
+    transaction_type: str  # 'flow', 'fixed', 'manual'
+    status: str
+    created_at: datetime
+    transaction_time: Optional[datetime] = None  # Original ATM transaction time
+    lamassu_transaction_id: Optional[str] = None
+
+
+# Internal Models for Client Dashboard (Database storage in centavos)
 class ClientDashboardSummary(BaseModel):
-    """Summary metrics for client dashboard overview"""
+    """Internal model - client dashboard summary stored in centavos"""
     user_id: str
     total_sats_accumulated: int
     total_fiat_invested: int  # Confirmed deposits (in centavos)
@@ -24,7 +54,7 @@ class ClientDashboardSummary(BaseModel):
 
 
 class ClientTransaction(BaseModel):
-    """Read-only view of client's DCA transactions"""
+    """Internal model - client transaction stored in centavos"""
     id: str
     amount_sats: int
     amount_fiat: int  # Stored in centavos (GTQ * 100) for precision