diff --git a/src/monitor_utils/database.py b/src/monitor_utils/database.py
index 3a0b9de..9c95c4b 100644
--- a/src/monitor_utils/database.py
+++ b/src/monitor_utils/database.py
@@ -347,6 +347,11 @@ def convert_product_to_mongo(product: Product) -> dict:
         "customizationIndex": metadata["customization_index"],
         "memberNonMemberComparison": metadata["member_non_member_comparison"],
         "overstockText": metadata["overstock_text"],
+        "affiliateUrl": metadata["affiliate_url"],
+        "promoCode": metadata["promo_code"],
+        "promoPercentage": metadata["promo_percentage"],
+        "promoDollarOff": metadata["promo_dollar_off"],
+        "promoMinSpend": metadata["promo_min_spend"],
         "startDate": timing["start_date"],
         "endDate": timing["end_date"],
         "priceBeforeDrop": pricing["price_before_drop"],
diff --git a/src/monitor_utils/runner.py b/src/monitor_utils/runner.py
index a9d528e..0358772 100644
--- a/src/monitor_utils/runner.py
+++ b/src/monitor_utils/runner.py
@@ -116,6 +116,27 @@ async def setup_config(
     return category_names, config["channels"], collection
 
 
+def combined_discount(base_percentage: int, promo_percentage: int | None) -> int:
+    """Combine an on-sale discount with a percentage code applied at checkout.
+
+    A "extra N% off" code discounts the already-reduced sale price, so the two
+    compound rather than add: 20% off then an extra 30% code is 44% off list,
+    not 50%. Returns base_percentage unchanged when there is no percentage code.
+
+    Args:
+        base_percentage: The on-sale discount off list, as a whole percent.
+        promo_percentage: The code's advertised percent off, or None.
+
+    Returns:
+        The combined discount off list, rounded to a whole percent.
+    """
+
+    if not promo_percentage:
+        return base_percentage
+
+    return round(100 - (100 - base_percentage) * (100 - promo_percentage) / 100)
+
+
 def build_product_details(
     product: dict,
     min_percentage: int,
@@ -148,7 +169,11 @@ def build_product_details(
 
     percentage = int(((original_price - current_price) / original_price) * 100)
     price_drop = original_price - current_price
-    passes_percentage = percentage >= min_percentage
+    # A percentage code compounds onto the sale price, so an item can clear the
+    # threshold on the combined discount even when the base discount would not.
+    # Dollar codes do not map to a percent and never affect the threshold.
+    effective_percentage = combined_discount(percentage, product.get("promoPercentage"))
+    passes_percentage = effective_percentage >= min_percentage
     passes_price_drop = min_price_drop is not None and price_drop >= min_price_drop
     if not passes_percentage and not passes_price_drop:
         return
@@ -164,6 +189,10 @@ def build_product_details(
             overstock_text=product["overstockText"],
             percentage=percentage,
             affiliate_url=product.get("affiliateUrl"),
+            promo_code=product.get("promoCode"),
+            promo_percentage=product.get("promoPercentage"),
+            promo_dollar_off=product.get("promoDollarOff"),
+            promo_min_spend=product.get("promoMinSpend"),
         ),
         timing=ProductTiming(
             discovered_date=product["discoveredDate"],
@@ -351,7 +380,7 @@ async def execute_pagination(
 
     async def fetch_page(page_index: int):
         """Fetch a single page or offset, optionally under the shared semaphore."""
-        async with (semaphore or nullcontext()):
+        async with semaphore or nullcontext():
             if stop_event.is_set():
                 return
 
diff --git a/tests/test_build_product_details.py b/tests/test_build_product_details.py
new file mode 100644
index 0000000..69ad098
--- /dev/null
+++ b/tests/test_build_product_details.py
@@ -0,0 +1,105 @@
+"""unit test: build_product_details thresholding, promo read, and combined_discount
+
+run from the repo root:
+    uv run pytest tests/test_build_product_details.py
+
+pure and offline — no Mongo. Builds a Product from a raw doc dict and checks the
+discount threshold (with percentage codes compounding onto the sale price), the
+promo fields read through via .get, and the combined_discount helper.
+"""
+
+from datetime import datetime, timezone
+
+from monitor_utils.runner import build_product_details, combined_discount
+
+
+def _doc(**overrides) -> dict:
+    """A well-formed product doc; override prices/promo per test."""
+    doc = {
+        "_id": "p1_tools",
+        "title": "Widget",
+        "url": "http://x/p1",
+        "currentPrice": 80.0,
+        "originalPrice": 100.0,
+        "imageUrl": "http://img/1",
+        "customizationIndex": None,
+        "memberNonMemberComparison": None,
+        "overstockText": None,
+        "discoveredDate": datetime(2026, 7, 26, tzinfo=timezone.utc),
+        "startDate": None,
+        "endDate": None,
+        "priceBeforeDrop": None,
+        "eduPrice": None,
+        "available": True,
+        "condition": None,
+        "appExclusive": None,
+        "memberPick": None,
+        "memberDeal": None,
+    }
+    doc.update(overrides)
+    return doc
+
+
+# ------------------------------------------------------------ combined_discount
+
+
+def test_combined_discount_no_promo_is_base():
+    assert combined_discount(24, None) == 24
+    assert combined_discount(24, 0) == 24
+
+
+def test_combined_discount_compounds_not_adds():
+    # 20% off then extra 30% code -> 44% off list (customer pays $56), not 50%
+    assert combined_discount(20, 30) == 44
+
+
+def test_combined_discount_rounds_to_nearest():
+    # 24% sale + 22% code: 1 - .76*.78 = .4072 -> 41 (rounded, not truncated 40)
+    assert combined_discount(24, 22) == 41
+
+
+# --------------------------------------------------------- build_product_details
+
+
+def test_promo_fields_read_through():
+    doc = _doc(
+        promoCode="BIRTHDAY26",
+        promoPercentage=22,
+        promoDollarOff=None,
+        promoMinSpend=None,
+    )
+    product = build_product_details(doc, min_percentage=0)
+    assert product.metadata.promo_code == "BIRTHDAY26"
+    assert product.metadata.promo_percentage == 22
+    # base percentage is the raw price delta, unchanged by the code
+    assert product.metadata.percentage == 20
+
+
+def test_missing_promo_keys_default_to_none():
+    """a doc from a lagging monitor lacks promo keys -> None, not KeyError"""
+    product = build_product_details(_doc(), min_percentage=0)
+    assert product.metadata.promo_code is None
+    assert product.metadata.promo_percentage is None
+
+
+def test_percentage_code_lifts_item_over_threshold():
+    # 30% base fails min 40, but +22% code -> 45% combined clears it
+    doc = _doc(currentPrice=70.0, originalPrice=100.0, promoPercentage=22)
+    assert build_product_details(doc, min_percentage=40) is not None
+
+
+def test_below_threshold_without_code_is_skipped():
+    doc = _doc(currentPrice=70.0, originalPrice=100.0)  # 30%, no code
+    assert build_product_details(doc, min_percentage=40) is None
+
+
+def test_dollar_code_does_not_affect_threshold():
+    # a dollar code has no promoPercentage, so 30% base stays below min 40
+    doc = _doc(
+        currentPrice=70.0,
+        originalPrice=100.0,
+        promoCode="STORE22",
+        promoDollarOff=22,
+        promoMinSpend=100,
+    )
+    assert build_product_details(doc, min_percentage=40) is None