diff --git a/tradein-mvp/backend/app/services/estimator.py b/tradein-mvp/backend/app/services/estimator.py
index 0bd631bf..309dc90b 100644
--- a/tradein-mvp/backend/app/services/estimator.py
+++ b/tradein-mvp/backend/app/services/estimator.py
@@ -1759,7 +1759,18 @@ def _filter_outliers(lots: list[dict[str, Any]]) -> list[dict[str, Any]]:
     low = q1 - 1.5 * iqr
     high = q3 + 1.5 * iqr
 
-    clean = [lot for lot in lots if low <= lot.get("price_per_m2", 0) <= high]
+    # None-safe: listings.price_per_m2 is nullable, и lot.get(..., 0) вернёт None
+    # (а не дефолт 0) когда ключ ПРИСУТСТВУЕТ со значением None → low <= None <= high
+    # бросает TypeError в Python 3. Лоты без цены судить как outlier нечем — оставляем их.
+    clean = []
+    for lot in lots:
+        ppm2 = lot.get("price_per_m2")
+        if ppm2 is None:
+            clean.append(lot)  # нечего сравнивать — keep
+            continue
+        if low <= ppm2 <= high:
+            clean.append(lot)  # priced лот внутри Tukey-границ — keep
+        # else: priced outlier за пределами границ — drop
     if len(clean) < len(lots):
         logger.info("outlier filter: %d → %d (Q1=%d Q3=%d)", len(lots), len(clean), q1, q3)
     return clean
diff --git a/tradein-mvp/backend/tests/test_estimator_pure_units.py b/tradein-mvp/backend/tests/test_estimator_pure_units.py
new file mode 100644
index 00000000..3fbbce4e
--- /dev/null
+++ b/tradein-mvp/backend/tests/test_estimator_pure_units.py
@@ -0,0 +1,293 @@
+"""Unit tests for the estimator's pure numeric helpers (issue #580).
+
+Covers the three side-effect-free functions:
+  - estimator._percentile      — linear-interpolation percentile
+  - estimator._filter_outliers — Tukey 1.5×IQR outlier filter (None-safe)
+  - estimator._compute_confidence — confidence level + explanation string
+
+No DB / network / mocks: these helpers operate on plain lists/dicts.
+
+NOTE: importing app.services.estimator pulls app.core.config.Settings, which
+requires DATABASE_URL. Set it BEFORE importing app modules (same pattern as
+tests/test_scheduler.py).
+"""
+import os
+
+os.environ.setdefault("DATABASE_URL", "postgresql+psycopg://test:test@localhost:5432/test")
+
+import pytest
+
+from app.services import estimator
+
+# --------------------------------------------------------------------------- #
+# _percentile
+# --------------------------------------------------------------------------- #
+# Assumes the input is ALREADY sorted ascending (documented in the source).
+# These tests pass pre-sorted lists accordingly.
+
+
+def test_percentile_empty_returns_zero() -> None:
+    assert estimator._percentile([], 0.5) == 0.0
+
+
+def test_percentile_single_element_returns_that_element_as_float() -> None:
+    result = estimator._percentile([42], 0.5)
+    assert result == 42.0
+    assert isinstance(result, float)
+
+
+def test_percentile_p0_returns_first_p1_returns_last() -> None:
+    values = [10.0, 20.0, 30.0, 40.0]
+    assert estimator._percentile(values, 0.0) == 10.0
+    assert estimator._percentile(values, 1.0) == 40.0
+
+
+def test_percentile_median_odd_length() -> None:
+    assert estimator._percentile([10, 20, 30], 0.5) == 20.0
+
+
+def test_percentile_median_even_length_interpolates() -> None:
+    # rank = 0.5 * (2 - 1) = 0.5 → 10 + (20 - 10) * 0.5 = 15.0
+    assert estimator._percentile([10, 20], 0.5) == 15.0
+
+
+def test_percentile_known_interpolation_case() -> None:
+    # [100, 200, 300, 400] at p=0.25:
+    #   rank = 0.25 * 3 = 0.75 → lo=0, hi=1, frac=0.75
+    #   100 + (200 - 100) * 0.75 = 175.0
+    assert estimator._percentile([100, 200, 300, 400], 0.25) == 175.0
+
+
+def test_percentile_does_not_mutate_input() -> None:
+    values = [10, 20, 30, 40]
+    snapshot = list(values)
+    estimator._percentile(values, 0.5)
+    assert values == snapshot
+
+
+# --------------------------------------------------------------------------- #
+# _filter_outliers
+# --------------------------------------------------------------------------- #
+
+
+def _lot(ppm2: float | None) -> dict:
+    """Build a minimal lot dict with the price_per_m2 key present."""
+    return {"price_per_m2": ppm2}
+
+
+def test_filter_outliers_passthrough_below_5_lots() -> None:
+    lots = [_lot(100), _lot(200), _lot(300), _lot(400)]
+    assert estimator._filter_outliers(lots) is lots  # returned unchanged
+
+
+def test_filter_outliers_passthrough_fewer_than_4_priced() -> None:
+    # 5 lots but only 3 carry a usable price → passthrough (cannot compute IQR)
+    lots = [_lot(100), _lot(200), _lot(300), _lot(None), _lot(0)]
+    assert estimator._filter_outliers(lots) is lots
+
+
+def test_filter_outliers_removes_high_outlier() -> None:
+    tight = [_lot(100), _lot(102), _lot(101), _lot(99), _lot(100)]
+    outlier = _lot(10_000)
+    lots = [*tight, outlier]
+    result = estimator._filter_outliers(lots)
+    assert outlier not in result
+    for lot in tight:
+        assert lot in result
+
+
+def test_filter_outliers_removes_low_outlier() -> None:
+    tight = [_lot(1000), _lot(1010), _lot(990), _lot(1005), _lot(995)]
+    outlier = _lot(1)
+    lots = [*tight, outlier]
+    result = estimator._filter_outliers(lots)
+    assert outlier not in result
+    for lot in tight:
+        assert lot in result
+
+
+def test_filter_outliers_none_priced_lot_does_not_raise_and_survives() -> None:
+    # Regression for issue #580: a lot where price_per_m2 key is PRESENT but None
+    # used to crash _filter_outliers with `low <= None <= high` → TypeError.
+    tight = [_lot(100), _lot(102), _lot(101), _lot(99), _lot(100)]
+    none_lot = _lot(None)
+    high_outlier = _lot(10_000)
+    lots = [*tight, none_lot, high_outlier]
+
+    # Must not raise.
+    result = estimator._filter_outliers(lots)
+
+    # The None-priced lot has no price to judge → retained.
+    assert none_lot in result
+    # Genuine priced outlier still dropped.
+    assert high_outlier not in result
+    # Tight cluster retained.
+    for lot in tight:
+        assert lot in result
+
+
+def test_filter_outliers_all_identical_prices_removes_nothing() -> None:
+    # IQR == 0 → bounds collapse to the single value, every lot equals it.
+    lots = [_lot(500) for _ in range(6)]
+    result = estimator._filter_outliers(lots)
+    assert len(result) == len(lots)
+
+
+# --------------------------------------------------------------------------- #
+# _compute_confidence
+# --------------------------------------------------------------------------- #
+
+
+def _addr_lots(addresses: list[str]) -> list[dict]:
+    """Build listings dicts carrying just an `address` key."""
+    return [{"address": addr} for addr in addresses]
+
+
+def test_confidence_zero_median_returns_low_no_analogs_message() -> None:
+    level, explanation = estimator._compute_confidence(
+        n_analogs=0,
+        median_ppm2=0,
+        q1=0,
+        q3=0,
+        fallback_radius_used=False,
+    )
+    assert level == "low"
+    assert "не найдено аналогов" in explanation.lower()
+
+
+def test_confidence_high_with_7_unique_addresses_and_tight_iqr() -> None:
+    # 7 unique addresses, IQR/median = (105-95)/100 = 0.10 < 0.15 → high.
+    # avg_lots_per_addr = 7 / 7 = 1.0 (no downgrade).
+    listings = _addr_lots([f"ул. Тестовая, {i}" for i in range(7)])
+    level, _ = estimator._compute_confidence(
+        n_analogs=7,
+        median_ppm2=100,
+        q1=95,
+        q3=105,
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "high"
+
+
+def test_confidence_medium_via_4_unique_addresses() -> None:
+    # 4 unique addresses → medium branch (independent of IQR).
+    # Wide IQR ensures it is NOT "high". avg = 4/4 = 1.0 (no downgrade).
+    listings = _addr_lots(["a", "b", "c", "d"])
+    level, _ = estimator._compute_confidence(
+        n_analogs=4,
+        median_ppm2=100,
+        q1=70,
+        q3=130,  # IQR/median = 0.60 → not high
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "medium"
+
+
+def test_confidence_medium_via_2_unique_addresses_and_tight_iqr() -> None:
+    # 2 unique addresses AND IQR/median = 0.20 < 0.25 → medium.
+    # avg = 2/2 = 1.0 (no downgrade).
+    listings = _addr_lots(["a", "b"])
+    level, _ = estimator._compute_confidence(
+        n_analogs=2,
+        median_ppm2=100,
+        q1=90,
+        q3=110,
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "medium"
+
+
+def test_confidence_low_single_address_wide_iqr() -> None:
+    listings = _addr_lots(["a"])
+    level, _ = estimator._compute_confidence(
+        n_analogs=1,
+        median_ppm2=100,
+        q1=50,
+        q3=150,  # IQR/median = 1.0
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "low"
+
+
+def test_confidence_downgrade_on_concentration_bias() -> None:
+    # 10 analogs across only 3 unique addresses:
+    #   unique_addr_count = 3, IQR/median = 0.20 < 0.25 → base = "medium"
+    #   avg_lots_per_addr = 10 / 3 = 3.33 > 2.5 → downgrade medium → low
+    listings = _addr_lots(["a", "b", "c"])
+    level, explanation = estimator._compute_confidence(
+        n_analogs=10,
+        median_ppm2=100,
+        q1=90,
+        q3=110,
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "low"
+    # Explanation should flag the concentration / bias.
+    assert "bias" in explanation.lower() or "на адрес" in explanation.lower()
+
+
+def test_confidence_downgrade_high_to_medium() -> None:
+    # High profile (7 unique addrs, tight IQR) but heavily concentrated:
+    #   n_analogs = 30, unique = 7 → avg = 4.28 > 2.5 → downgrade high → medium.
+    listings = _addr_lots([f"addr-{i}" for i in range(7)])
+    level, explanation = estimator._compute_confidence(
+        n_analogs=30,
+        median_ppm2=100,
+        q1=95,
+        q3=105,  # IQR/median = 0.10 < 0.15
+        fallback_radius_used=False,
+        listings=listings,
+    )
+    assert level == "medium"
+    assert "bias" in explanation.lower() or "на адрес" in explanation.lower()
+
+
+def test_confidence_fallback_radius_mentions_radius() -> None:
+    listings = _addr_lots(["a", "b", "c", "d"])
+    _, explanation = estimator._compute_confidence(
+        n_analogs=4,
+        median_ppm2=100,
+        q1=90,
+        q3=110,
+        fallback_radius_used=True,
+        listings=listings,
+    )
+    assert "радиус" in explanation.lower()
+
+
+def test_confidence_area_widened_mentions_area() -> None:
+    listings = _addr_lots(["a", "b", "c", "d"])
+    _, explanation = estimator._compute_confidence(
+        n_analogs=4,
+        median_ppm2=100,
+        q1=90,
+        q3=110,
+        fallback_radius_used=False,
+        area_widened=True,
+        listings=listings,
+    )
+    assert "площад" in explanation.lower()
+
+
+def test_confidence_listings_none_uses_n_analogs_as_unique_count() -> None:
+    # listings=None path: unique_addr_count = n_analogs, avg_lots_per_addr = 1.0
+    # (no crash, no downgrade). 4 "unique" → medium.
+    level, explanation = estimator._compute_confidence(
+        n_analogs=4,
+        median_ppm2=100,
+        q1=90,
+        q3=110,
+        fallback_radius_used=False,
+        listings=None,
+    )
+    assert level == "medium"
+    assert "4" in explanation  # n_analogs surfaced in the message
+
+
+if __name__ == "__main__":  # pragma: no cover
+    raise SystemExit(pytest.main([__file__, "-q"]))