diff --git a/changelog.d/mtr-uncomputed-adults.added.md b/changelog.d/mtr-uncomputed-adults.added.md
new file mode 100644
index 00000000000..8a287e66b06
--- /dev/null
+++ b/changelog.d/mtr-uncomputed-adults.added.md
@@ -0,0 +1 @@
+Add `marginal_tax_rate_computed`, which flags the people whose marginal tax rates are simulated (the top `simulation.marginal_tax_rate_adults` earners among each household's adults); the marginal tax rate variables are a placeholder zero for everyone else.
diff --git a/changelog.d/mtr-uncomputed-adults.fixed.md b/changelog.d/mtr-uncomputed-adults.fixed.md
new file mode 100644
index 00000000000..7cfb6daf93d
--- /dev/null
+++ b/changelog.d/mtr-uncomputed-adults.fixed.md
@@ -0,0 +1 @@
+Fix `cliff_evaluated` to rank adults by market income, as the marginal tax rate loop does, instead of by age.
diff --git a/policyengine_us/parameters/simulation/marginal_tax_rate_adults.yaml b/policyengine_us/parameters/simulation/marginal_tax_rate_adults.yaml
index 1f1ae60a4d1..2d4bb345bc4 100644
--- a/policyengine_us/parameters/simulation/marginal_tax_rate_adults.yaml
+++ b/policyengine_us/parameters/simulation/marginal_tax_rate_adults.yaml
@@ -1,4 +1,4 @@
-description: Number of adults to simulate a marginal tax rate for, in each household.
+description: Number of adults in each household, ranked by market income, for whom the earnings marginal tax rates are simulated. Everyone else gets a marginal tax rate of zero; marginal_tax_rate_computed flags who is simulated.
 values:
   0000-01-01: 2
 metadata:
diff --git a/policyengine_us/tests/core/test_marginal_tax_rate_coverage.py b/policyengine_us/tests/core/test_marginal_tax_rate_coverage.py
new file mode 100644
index 00000000000..bb75598951f
--- /dev/null
+++ b/policyengine_us/tests/core/test_marginal_tax_rate_coverage.py
@@ -0,0 +1,195 @@
+"""Invariants of which people get a simulated marginal tax rate.
+
+The marginal tax rate variables run one branch simulation per adult rank, from
+1 to simulation.marginal_tax_rate_adults, perturbing the adult whose
+adult_earnings_index (rank by market income within the household) equals that
+rank. Everyone else keeps a placeholder of zero. marginal_tax_rate_computed
+flags the simulated people, and cliff_evaluated must agree with it because the
+cliff gap is derived from marginal_tax_rate.
+
+Every household in a grid of adult counts, earnings orders, ties, negative
+market income, teen earners and children shares one simulation per cap, and is
+checked against that rule, restated here without adult_earnings_index:
+
+1. Each household flags min(cap, adults) people, all adults, and every flagged
+   adult has at least the market income of every unflagged adult.
+2. cliff_evaluated equals marginal_tax_rate_computed.
+3. Every marginal tax rate variable is exactly zero wherever the flag is false.
+4. Raising the cap only adds people: anyone flagged under a lower cap keeps the
+   same flag and the same marginal tax rates under a higher one. This holds with
+   behavioral responses off, as here; with labor supply responses on, the cap
+   changes measured marginal tax rates and so earnings and ranks.
+"""
+
+from itertools import product
+
+import numpy as np
+import pytest
+from policyengine_core.reforms import Reform
+
+from policyengine_us import Simulation
+
+YEAR = 2024
+CAP = "simulation.marginal_tax_rate_adults"
+# One variable per code path: the net income loop, its health-benefit copy, and
+# the component helper shared by the federal, state and FICA variables.
+MTR_VARIABLES = (
+    "marginal_tax_rate",
+    "marginal_tax_rate_including_health_benefits",
+    "federal_marginal_tax_rate",
+)
+# Employment income per adult; a negative entry is a self-employment loss, which
+# makes that adult's market income negative.
+ADULT_EARNINGS = (
+    (0,),
+    (40_000,),
+    (80_000, 0),
+    (0, 80_000),
+    (50_000, 50_000),
+    (0, 0, 0),
+    (30_000, 90_000, 60_000),
+    (20_000, 0, 20_000, 70_000),
+    (10_000, 45_000, 0, 45_000, 120_000),
+    (-20_000, 30_000),
+    (10_000, -5_000, 0, 60_000),
+)
+TEEN_EARNINGS = (None, 0, 8_000)
+HAS_CHILD = (False, True)
+
+
+def _situation():
+    people, tax_units, spm_units, households = {}, {}, {}, {}
+    shapes = product(ADULT_EARNINGS, TEEN_EARNINGS, HAS_CHILD)
+    for h, (adults, teen, child) in enumerate(shapes):
+        members = []
+        for a, earnings in enumerate(adults):
+            name = f"h{h}_adult{a}"
+            income = "employment_income" if earnings >= 0 else "self_employment_income"
+            people[name] = {"age": {YEAR: 25 + 7 * a}, income: {YEAR: earnings}}
+            tax_units[f"{name}_tax_unit"] = {"members": [name]}
+            members.append(name)
+        dependents = []
+        if teen is not None:
+            dependents.append(f"h{h}_teen")
+            people[f"h{h}_teen"] = {
+                "age": {YEAR: 16},
+                "employment_income": {YEAR: teen},
+            }
+        if child:
+            dependents.append(f"h{h}_child")
+            people[f"h{h}_child"] = {"age": {YEAR: 6}}
+        tax_units[f"h{h}_adult0_tax_unit"]["members"] += dependents
+        members += dependents
+        spm_units[f"h{h}_spm_unit"] = {"members": members}
+        households[f"h{h}"] = {"members": members, "state_code": {YEAR: "TX"}}
+    return {
+        "people": people,
+        "tax_units": tax_units,
+        "spm_units": spm_units,
+        "households": households,
+    }
+
+
+def _simulation(cap):
+    return Simulation(
+        situation=_situation(),
+        reform=Reform.from_dict({CAP: {str(YEAR): cap}}, country_id="us"),
+    )
+
+
+def _calc(simulation, variable):
+    return np.asarray(simulation.calculate(variable, YEAR))
+
+
+@pytest.fixture(scope="module")
+def households():
+    simulation = _simulation(0)
+    return {
+        "household_id": simulation.populations["household"].members_entity_id,
+        "is_adult": _calc(simulation, "is_adult").astype(bool),
+        "market_income": _calc(simulation, "market_income"),
+    }
+
+
+@pytest.mark.parametrize("cap", [0, 1, 2, 3, 5])
+def test_flag_selects_the_top_earning_adults(households, cap):
+    simulation = _simulation(cap)
+    flag = _calc(simulation, "marginal_tax_rate_computed").astype(bool)
+    assert np.array_equal(_calc(simulation, "cliff_evaluated").astype(bool), flag)
+    assert not flag[~households["is_adult"]].any()
+    for household_id in np.unique(households["household_id"]):
+        in_household = households["household_id"] == household_id
+        adults = in_household & households["is_adult"]
+        flagged = in_household & flag
+        assert flagged.sum() == min(cap, adults.sum())
+        unflagged_adults = adults & ~flag
+        if flagged.any() and unflagged_adults.any():
+            income = households["market_income"]
+            assert income[flagged].min() >= income[unflagged_adults].max()
+
+
+@pytest.fixture(scope="module")
+def mtr_by_cap():
+    results = {}
+    for cap in (2, 3):
+        simulation = _simulation(cap)
+        results[cap] = {
+            variable: _calc(simulation, variable)
+            for variable in ("marginal_tax_rate_computed",) + MTR_VARIABLES
+        }
+    return results
+
+
+@pytest.mark.parametrize("variable", MTR_VARIABLES)
+def test_unsimulated_people_get_a_placeholder_zero(mtr_by_cap, variable):
+    for results in mtr_by_cap.values():
+        flag = results["marginal_tax_rate_computed"].astype(bool)
+        assert (results[variable][~flag] == 0).all()
+
+
+@pytest.mark.parametrize("variable", MTR_VARIABLES)
+def test_raising_the_cap_only_adds_people(mtr_by_cap, variable):
+    lower, higher = mtr_by_cap[2], mtr_by_cap[3]
+    lower_flag = lower["marginal_tax_rate_computed"].astype(bool)
+    higher_flag = higher["marginal_tax_rate_computed"].astype(bool)
+    assert (higher_flag[lower_flag]).all()
+    assert higher_flag.sum() > lower_flag.sum()
+    assert np.array_equal(lower[variable][lower_flag], higher[variable][lower_flag])
+
+
+# Three single roommates in Texas in 2024, each filing alone. Taxable income is
+# wages less the $14,600 standard deduction ($75,400, $45,400, $15,400), so a
+# $1,000 raise is taxed at 22%, 12% and 12%, plus 7.65% employee payroll tax.
+# Nobody crosses a bracket or payroll threshold, and Texas has no income tax.
+ROOMMATE_WAGES = (90_000, 60_000, 30_000)
+ROOMMATE_RATES = {
+    "marginal_tax_rate": (0.2965, 0.1965, 0.1965),
+    "federal_marginal_tax_rate": (0.22, 0.12, 0.12),
+    "fica_marginal_tax_rate": (0.0765, 0.0765, 0.0765),
+    "state_marginal_tax_rate": (0, 0, 0),
+}
+
+
+@pytest.mark.parametrize("cap", [2, 3])
+def test_roommates_match_hand_computed_rates(cap):
+    names = [f"roommate{i}" for i in range(len(ROOMMATE_WAGES))]
+    situation = {
+        "people": {
+            name: {"age": {YEAR: 40 - 5 * i}, "employment_income": {YEAR: wages}}
+            for i, (name, wages) in enumerate(zip(names, ROOMMATE_WAGES))
+        },
+        "tax_units": {f"{name}_tax_unit": {"members": [name]} for name in names},
+        "spm_units": {f"{name}_spm_unit": {"members": [name]} for name in names},
+        "households": {"home": {"members": names, "state_code": {YEAR: "TX"}}},
+    }
+    simulation = Simulation(
+        situation=situation,
+        reform=Reform.from_dict({CAP: {str(YEAR): cap}}, country_id="us"),
+    )
+    simulated = np.arange(len(names)) < cap
+    assert np.array_equal(
+        _calc(simulation, "marginal_tax_rate_computed").astype(bool), simulated
+    )
+    for variable, rates in ROOMMATE_RATES.items():
+        expected = np.where(simulated, rates, 0)
+        assert np.allclose(_calc(simulation, variable), expected, atol=1e-4)
diff --git a/policyengine_us/tests/policy/baseline/household/cliff_evaluated.yaml b/policyengine_us/tests/policy/baseline/household/cliff_evaluated.yaml
index fe9a4312347..6b4bbb036aa 100644
--- a/policyengine_us/tests/policy/baseline/household/cliff_evaluated.yaml
+++ b/policyengine_us/tests/policy/baseline/household/cliff_evaluated.yaml
@@ -65,3 +65,25 @@
         members: [person1, person2, person3]
   output:
     cliff_evaluated: [true, true, true]
+
+- name: cliff_evaluated follows earnings rank, not age, like marginal_tax_rate
+  period: 2024
+  input:
+    people:
+      person1:
+        age: 70
+      person2:
+        age: 40
+        employment_income: 80_000
+      person3:
+        age: 38
+        employment_income: 50_000
+      person4:
+        age: 22
+        employment_income: 30_000
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: TX
+  output:
+    cliff_evaluated: [false, true, true, false]
diff --git a/policyengine_us/tests/policy/baseline/household/marginal_tax_rate.yaml b/policyengine_us/tests/policy/baseline/household/marginal_tax_rate.yaml
index c6fc58a09cb..8ad352eb148 100644
--- a/policyengine_us/tests/policy/baseline/household/marginal_tax_rate.yaml
+++ b/policyengine_us/tests/policy/baseline/household/marginal_tax_rate.yaml
@@ -35,7 +35,7 @@
   absolute_error_margin: 0.0001
   period: 2021
   input:
-    simulation.marginal_tax_rate_adults: 1  # the default value
+    simulation.marginal_tax_rate_adults: 1  # below the default of 2
     people:
       person1:
         age: 43
@@ -88,3 +88,49 @@
         state_fips: 48  # TX
   output:
     marginal_tax_rate: [0.3165, -0.0765]
+
+# Three single roommates in Texas in 2024, each filing alone. Taxable income is
+# earnings less the $14,600 standard deduction, so the $90,000 earner is in the
+# 22% bracket and the $60,000 and $30,000 earners are in the 12% bracket; each
+# also pays 7.65% employee payroll tax. The federal and FICA components check the
+# shared component helper, which has its own copy of the adult loop.
+# The same household with the cap raised to 3 is in
+# tests/core/test_marginal_tax_rate_coverage.py, which avoids another cached
+# tax-benefit system in the batched YAML runner.
+- name: Third earner in a household gets a placeholder zero under the default cap
+  absolute_error_margin: 0.0001
+  period: 2024
+  input:
+    people:
+      person1:
+        age: 40
+        employment_income: 90_000
+      person2:
+        age: 35
+        employment_income: 60_000
+      person3:
+        age: 30
+        employment_income: 30_000
+    tax_units:
+      tax_unit1:
+        members: [person1]
+      tax_unit2:
+        members: [person2]
+      tax_unit3:
+        members: [person3]
+    spm_units:
+      spm_unit1:
+        members: [person1]
+      spm_unit2:
+        members: [person2]
+      spm_unit3:
+        members: [person3]
+    households:
+      household:
+        members: [person1, person2, person3]
+        state_code: TX
+  output:
+    marginal_tax_rate: [0.2965, 0.1965, 0]
+    marginal_tax_rate_computed: [true, true, false]
+    federal_marginal_tax_rate: [0.22, 0.12, 0]
+    fica_marginal_tax_rate: [0.0765, 0.0765, 0]
diff --git a/policyengine_us/tests/policy/baseline/household/marginal_tax_rate_computed.yaml b/policyengine_us/tests/policy/baseline/household/marginal_tax_rate_computed.yaml
new file mode 100644
index 00000000000..cf66b77d6fe
--- /dev/null
+++ b/policyengine_us/tests/policy/baseline/household/marginal_tax_rate_computed.yaml
@@ -0,0 +1,49 @@
+# The marginal tax rate loop simulates adults whose adult_earnings_index (rank
+# by market income within the household) is 1 through
+# simulation.marginal_tax_rate_adults; everyone else gets a placeholder zero.
+# Cases here use the default cap of 2: every distinct parameter override pins
+# another copy of the tax-benefit system in the batched YAML runner, so cases
+# that vary the cap live in tests/core/test_marginal_tax_rate_coverage.py.
+
+- name: Default cap simulates the top two earners, not the two oldest adults
+  period: 2024
+  input:
+    people:
+      person1:
+        age: 70
+      person2:
+        age: 40
+        employment_income: 80_000
+      person3:
+        age: 38
+        employment_income: 50_000
+      person4:
+        age: 22
+        employment_income: 30_000
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: TX
+  output:
+    adult_earnings_index: [4, 1, 2, 3]
+    marginal_tax_rate_computed: [false, true, true, false]
+
+- name: Children are never simulated, even with earnings and room under the cap
+  period: 2024
+  input:
+    people:
+      person1:
+        age: 40
+        employment_income: 60_000
+      person2:
+        age: 16
+        employment_income: 8_000
+      person3:
+        age: 10
+    households:
+      household:
+        members: [person1, person2, person3]
+        state_code: TX
+  output:
+    adult_earnings_index: [1, 0, 0]
+    marginal_tax_rate_computed: [true, false, false]
diff --git a/policyengine_us/variables/gov/simulation/capital_gains_responses.py b/policyengine_us/variables/gov/simulation/capital_gains_responses.py
index d39a372f76a..cf19dfcb2e7 100644
--- a/policyengine_us/variables/gov/simulation/capital_gains_responses.py
+++ b/policyengine_us/variables/gov/simulation/capital_gains_responses.py
@@ -86,6 +86,9 @@ class marginal_tax_rate_on_capital_gains(Variable):
     label = "capital gains marginal tax rate"
     documentation = (
         "Percent of marginal capital gains that do not increase household net income."
+        " Simulated only for the two adults in each household with the largest"
+        " long-term capital gains (adult_index_cg 1 and 2), regardless of"
+        " simulation.marginal_tax_rate_adults; zero for everyone else."
     )
     entity = Person
     definition_period = YEAR
diff --git a/policyengine_us/variables/household/cliff.py b/policyengine_us/variables/household/cliff.py
index 28f24445a93..984ff7f5ca7 100644
--- a/policyengine_us/variables/household/cliff.py
+++ b/policyengine_us/variables/household/cliff.py
@@ -9,10 +9,9 @@ class cliff_evaluated(Variable):
     definition_period = YEAR
 
     def formula(person, period, parameters):
-        adult_index_values = person("adult_index", period)
-        mtr_adult_count = parameters(period).simulation.marginal_tax_rate_adults
-        is_adult = person("is_adult", period)
-        return is_adult & (adult_index_values <= mtr_adult_count)
+        # The cliff gap comes from marginal_tax_rate, so it is simulated
+        # exactly where the marginal tax rate is.
+        return person("marginal_tax_rate_computed", period)
 
 
 class cliff_gap(Variable):
diff --git a/policyengine_us/variables/household/federal_marginal_tax_rate.py b/policyengine_us/variables/household/federal_marginal_tax_rate.py
index 5d6da27865a..34094a87d78 100644
--- a/policyengine_us/variables/household/federal_marginal_tax_rate.py
+++ b/policyengine_us/variables/household/federal_marginal_tax_rate.py
@@ -8,6 +8,9 @@ class federal_marginal_tax_rate(Variable):
     label = "federal marginal tax rate"
     documentation = (
         "Marginal change in federal income tax per dollar of additional earnings."
+        " Simulated only where marginal_tax_rate_computed is true: for up to"
+        " simulation.marginal_tax_rate_adults adults per household, those with"
+        " the highest market income. Zero for everyone else."
     )
     entity = Person
     definition_period = YEAR
diff --git a/policyengine_us/variables/household/fica_marginal_tax_rate.py b/policyengine_us/variables/household/fica_marginal_tax_rate.py
index d434d34cdd3..2dfa8b4655c 100644
--- a/policyengine_us/variables/household/fica_marginal_tax_rate.py
+++ b/policyengine_us/variables/household/fica_marginal_tax_rate.py
@@ -8,6 +8,9 @@ class fica_marginal_tax_rate(Variable):
     label = "FICA marginal tax rate"
     documentation = (
         "Marginal change in employee payroll tax per dollar of additional earnings."
+        " Simulated only where marginal_tax_rate_computed is true: for up to"
+        " simulation.marginal_tax_rate_adults adults per household, those with"
+        " the highest market income. Zero for everyone else."
     )
     entity = Person
     definition_period = YEAR
diff --git a/policyengine_us/variables/household/marginal_tax_rate.py b/policyengine_us/variables/household/marginal_tax_rate.py
index a0abd052d58..879241a29ab 100644
--- a/policyengine_us/variables/household/marginal_tax_rate.py
+++ b/policyengine_us/variables/household/marginal_tax_rate.py
@@ -5,6 +5,9 @@ class marginal_tax_rate(Variable):
     label = "marginal tax rate"
     documentation = (
         "Fraction of marginal income gains that do not increase household net income."
+        " Simulated only where marginal_tax_rate_computed is true: for up to"
+        " simulation.marginal_tax_rate_adults adults per household, those with"
+        " the highest market income. Zero for everyone else."
     )
     entity = Person
     definition_period = YEAR
diff --git a/policyengine_us/variables/household/marginal_tax_rate_computed.py b/policyengine_us/variables/household/marginal_tax_rate_computed.py
new file mode 100644
index 00000000000..917a754fc2e
--- /dev/null
+++ b/policyengine_us/variables/household/marginal_tax_rate_computed.py
@@ -0,0 +1,29 @@
+from policyengine_us.model_api import *
+
+
+class marginal_tax_rate_computed(Variable):
+    value_type = bool
+    entity = Person
+    label = "marginal tax rate computed"
+    documentation = (
+        "Whether marginal_tax_rate, marginal_tax_rate_including_health_benefits, "
+        "federal_marginal_tax_rate, state_marginal_tax_rate and "
+        "fica_marginal_tax_rate are simulated for this person. They are "
+        "simulated only for adults whose adult_earnings_index (rank by market "
+        "income within the household) is at most "
+        "simulation.marginal_tax_rate_adults. Everyone else, including "
+        "children with earnings, gets a zero that is a placeholder, not a "
+        "simulated result. Filter on this flag before summarizing those "
+        "variables across people. marginal_tax_rate_on_capital_gains ranks "
+        "adults separately and is not covered by this flag."
+    )
+    definition_period = YEAR
+
+    def formula(person, period, parameters):
+        adult_count = parameters(period).simulation.marginal_tax_rate_adults
+        adult_earnings_index = person("adult_earnings_index", period)
+        return (
+            person("is_adult", period)
+            & (adult_earnings_index >= 1)
+            & (adult_earnings_index <= adult_count)
+        )
diff --git a/policyengine_us/variables/household/marginal_tax_rate_including_health_benefits.py b/policyengine_us/variables/household/marginal_tax_rate_including_health_benefits.py
index 02fe206ca49..b6b5580fae0 100644
--- a/policyengine_us/variables/household/marginal_tax_rate_including_health_benefits.py
+++ b/policyengine_us/variables/household/marginal_tax_rate_including_health_benefits.py
@@ -5,6 +5,9 @@ class marginal_tax_rate_including_health_benefits(Variable):
     label = "Marginal tax rate including health benefits"
     documentation = (
         "Fraction of marginal income gains that do not increase household net income."
+        " Simulated only where marginal_tax_rate_computed is true: for up to"
+        " simulation.marginal_tax_rate_adults adults per household, those with"
+        " the highest market income. Zero for everyone else."
     )
     entity = Person
     definition_period = YEAR
diff --git a/policyengine_us/variables/household/state_marginal_tax_rate.py b/policyengine_us/variables/household/state_marginal_tax_rate.py
index 68071d3516f..d7f4a20fcd2 100644
--- a/policyengine_us/variables/household/state_marginal_tax_rate.py
+++ b/policyengine_us/variables/household/state_marginal_tax_rate.py
@@ -8,6 +8,9 @@ class state_marginal_tax_rate(Variable):
     label = "state marginal tax rate"
     documentation = (
         "Marginal change in state income tax per dollar of additional earnings."
+        " Simulated only where marginal_tax_rate_computed is true: for up to"
+        " simulation.marginal_tax_rate_adults adults per household, those with"
+        " the highest market income. Zero for everyone else."
     )
     entity = Person
     definition_period = YEAR