diff --git a/backend/engines/compute.py b/backend/engines/compute.py
new file mode 100644
index 0000000..e4c9249
--- /dev/null
+++ b/backend/engines/compute.py
@@ -0,0 +1,64 @@
+"""
+Headless Compute Engine — All deterministic math in one function call.
+
+compute_all() runs every deterministic agent in sequence and returns the
+complete bundled result. This is the function behind the /api/v1/calculate
+endpoint — designed for sub-50ms execution with zero LLM involvement.
+
+Use cases:
+    - Frontend real-time sliders that update as the user drags
+    - Comparison tools that need fast recalculation
+    - Batch processing without burning API quota
+    - Unit testing the math pipeline in isolation
+"""
+import sys
+import os
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from schemas.schemas import UserInput, ComputeAllOutput
+from engines.india_defaults import calculate_true_total_cost
+from agents.deterministic.financial_reality import calculate_affordability
+from agents.deterministic.scenario_simulation import run_all_scenarios
+from agents.deterministic.risk_scorer import calculate_risk_score
+
+
+def compute_all(user_input: UserInput) -> ComputeAllOutput:
+    """
+    Run every deterministic calculation and return the bundled result.
+
+    Execution order (respects dependencies):
+        1. india_defaults   — hidden cost breakdown (independent)
+        2. affordability    — EMI, ratios, cash flow (independent)
+        3. scenarios        — stress tests (depends on #2)
+        4. risk_score       — composite score (depends on #2 and #3)
+
+    Total execution time target: < 50ms on a single CPU core.
+    All functions are pure Python arithmetic with no I/O.
+    """
+    loan_amount = user_input.property_price - user_input.down_payment
+    if loan_amount < 0:
+        loan_amount = 0.0
+
+    india_costs = calculate_true_total_cost(
+        base_price=user_input.property_price,
+        state=user_input.state,
+        property_type=user_input.property_type.value,
+        loan_amount=loan_amount,
+        area_sqft=user_input.area_sqft if user_input.area_sqft else 1000,
+    )
+
+    financial_reality = calculate_affordability(user_input)
+    all_scenarios = run_all_scenarios(user_input, financial_reality)
+    risk_score = calculate_risk_score(
+        financial_reality=financial_reality,
+        all_scenarios=all_scenarios,
+        age=user_input.age,
+        tenure_years=user_input.tenure_years,
+    )
+
+    return ComputeAllOutput(
+        india_cost_breakdown=india_costs,
+        financial_reality=financial_reality,
+        all_scenarios=all_scenarios,
+        risk_score=risk_score,
+    )
diff --git a/backend/main.py b/backend/main.py
index 63c206e..1e8523a 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -48,6 +48,8 @@
 from agents.deterministic.risk_scorer import calculate_risk_score
 from engines.pdf_generator import generate_pdf
 from storage.gcs_client import upload_pdf
+# Headless compute engine (PR: headless-calculate-endpoint)
+from engines.compute import compute_all
 
 
 # ---------------------------------------------------------------------------
@@ -102,6 +104,29 @@ async def health_check():
     return {"status": "healthy", "service": "niv-ai-home-buying-advisor", "version": "1.0.0"}
 
 
+# ---------------------------------------------------------------------------
+# Headless calculate — pure math, no LLM, no auth required
+# ---------------------------------------------------------------------------
+
+@app.post("/api/v1/calculate", response_model=APIResponse)
+async def calculate_route(user_input: UserInput):
+    """
+    Headless deterministic calculation endpoint.
+    Runs all math agents and returns the bundled result.
+    No auth required — pure math, zero API budget cost.
+    Designed for frontend real-time sliders. Target: < 50ms.
+    """
+    try:
+        result = compute_all(user_input)
+        return APIResponse(
+            success=True,
+            message="Calculation complete",
+            data=result.model_dump(),
+        )
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"Calculation failed: {str(e)}")
+
+
 # ---------------------------------------------------------------------------
 # Session management
 # ---------------------------------------------------------------------------
diff --git a/backend/schemas/schemas.py b/backend/schemas/schemas.py
index 7724f9e..0381c21 100644
--- a/backend/schemas/schemas.py
+++ b/backend/schemas/schemas.py
@@ -576,4 +576,16 @@ class SessionStartResponse(BaseModel):
 class ConversationResponse(BaseModel):
     session_id: str
     conversation_output: ConversationOutput
-    updated_analysis: Optional[AnalysisResponse] = None
\ No newline at end of file
+    updated_analysis: Optional[AnalysisResponse] = None
+
+
+# -----------------------------------------------------------------------------
+# Headless compute engine output (PR: headless-calculate-endpoint)
+# -----------------------------------------------------------------------------
+
+class ComputeAllOutput(BaseModel):
+    """Bundled output of all deterministic calculations — no LLM involved."""
+    india_cost_breakdown: IndiaCostBreakdown
+    financial_reality: FinancialRealityOutput
+    all_scenarios: AllScenariosOutput
+    risk_score: RiskScoreOutput
\ No newline at end of file