diff --git a/api/routes/results_v2.py b/api/routes/results_v2.py
index d3dfe35..340886f 100644
--- a/api/routes/results_v2.py
+++ b/api/routes/results_v2.py
@@ -3,6 +3,8 @@
 from fastapi import APIRouter, Query, Depends
 from typing import Optional, Literal
 import json
+import os
+from datetime import datetime, timedelta
 
 from api.database import Database
 
@@ -14,6 +16,65 @@ def get_database() -> Database:
     return Database()
 
 
+def validate_and_resolve_dates(
+    start_date: Optional[str],
+    end_date: Optional[str]
+) -> tuple[str, str]:
+    """Validate and resolve date parameters.
+
+    Args:
+        start_date: Start date (YYYY-MM-DD) or None
+        end_date: End date (YYYY-MM-DD) or None
+
+    Returns:
+        Tuple of (resolved_start_date, resolved_end_date)
+
+    Raises:
+        ValueError: If dates are invalid
+    """
+    # Default lookback days
+    default_lookback = int(os.getenv("DEFAULT_RESULTS_LOOKBACK_DAYS", "30"))
+
+    # Handle None cases
+    if start_date is None and end_date is None:
+        # Default to last N days
+        end_dt = datetime.now()
+        start_dt = end_dt - timedelta(days=default_lookback)
+        return start_dt.strftime("%Y-%m-%d"), end_dt.strftime("%Y-%m-%d")
+
+    if start_date is None:
+        # Only end_date provided -> single date
+        start_date = end_date
+
+    if end_date is None:
+        # Only start_date provided -> single date
+        end_date = start_date
+
+    # Validate date formats
+    try:
+        start_dt = datetime.strptime(start_date, "%Y-%m-%d")
+        end_dt = datetime.strptime(end_date, "%Y-%m-%d")
+
+        # Ensure strict YYYY-MM-DD format (e.g., reject "2025-1-16")
+        if start_date != start_dt.strftime("%Y-%m-%d"):
+            raise ValueError(f"Invalid date format. Expected YYYY-MM-DD")
+        if end_date != end_dt.strftime("%Y-%m-%d"):
+            raise ValueError(f"Invalid date format. Expected YYYY-MM-DD")
+    except ValueError:
+        raise ValueError(f"Invalid date format. Expected YYYY-MM-DD")
+
+    # Validate order
+    if start_dt > end_dt:
+        raise ValueError("start_date must be <= end_date")
+
+    # Validate not future
+    now = datetime.now()
+    if start_dt.date() > now.date() or end_dt.date() > now.date():
+        raise ValueError("Cannot query future dates")
+
+    return start_date, end_date
+
+
 @router.get("/results")
 async def get_results(
     job_id: Optional[str] = None,
diff --git a/tests/api/test_results_v2.py b/tests/api/test_results_v2.py
new file mode 100644
index 0000000..6c5dfa8
--- /dev/null
+++ b/tests/api/test_results_v2.py
@@ -0,0 +1,61 @@
+"""Tests for results_v2 endpoint date validation."""
+
+import pytest
+from datetime import datetime, timedelta
+from api.routes.results_v2 import validate_and_resolve_dates
+
+
+def test_validate_no_dates_provided():
+    """Test default to last 30 days when no dates provided."""
+    start, end = validate_and_resolve_dates(None, None)
+
+    # Should default to last 30 days
+    end_dt = datetime.strptime(end, "%Y-%m-%d")
+    start_dt = datetime.strptime(start, "%Y-%m-%d")
+
+    assert (end_dt - start_dt).days == 30
+    assert end_dt.date() <= datetime.now().date()
+
+
+def test_validate_only_start_date():
+    """Test single date when only start_date provided."""
+    start, end = validate_and_resolve_dates("2025-01-16", None)
+
+    assert start == "2025-01-16"
+    assert end == "2025-01-16"
+
+
+def test_validate_only_end_date():
+    """Test single date when only end_date provided."""
+    start, end = validate_and_resolve_dates(None, "2025-01-16")
+
+    assert start == "2025-01-16"
+    assert end == "2025-01-16"
+
+
+def test_validate_both_dates():
+    """Test date range when both provided."""
+    start, end = validate_and_resolve_dates("2025-01-16", "2025-01-20")
+
+    assert start == "2025-01-16"
+    assert end == "2025-01-20"
+
+
+def test_validate_invalid_date_format():
+    """Test error on invalid date format."""
+    with pytest.raises(ValueError, match="Invalid date format"):
+        validate_and_resolve_dates("2025-1-16", "2025-01-20")
+
+
+def test_validate_start_after_end():
+    """Test error when start_date > end_date."""
+    with pytest.raises(ValueError, match="start_date must be <= end_date"):
+        validate_and_resolve_dates("2025-01-20", "2025-01-16")
+
+
+def test_validate_future_date():
+    """Test error when dates are in future."""
+    future = (datetime.now() + timedelta(days=10)).strftime("%Y-%m-%d")
+
+    with pytest.raises(ValueError, match="Cannot query future dates"):
+        validate_and_resolve_dates(future, future)