diff --git a/settings.cfg b/settings.cfg
index 040d6e2..f8d1a3b 100644
--- a/settings.cfg
+++ b/settings.cfg
@@ -8,6 +8,6 @@
 --icu-rate 0.0075
 --market_share 0.15
 --n-days 60
---susceptible 4119405
+--population 4119405
 --ventilated-los 10
 --ventilated-rate 0.005
diff --git a/src/penn_chime/cli.py b/src/penn_chime/cli.py
index 4fed0f7..a4ec533 100644
--- a/src/penn_chime/cli.py
+++ b/src/penn_chime/cli.py
@@ -91,7 +91,7 @@ def parse_args():
             1.0,
             "Social Distancing Reduction Rate: 0.0 - 1.0",
         ),
-        ("--susceptible", int, 1, None, "Regional Population >= 1"),
+        ("--population", int, 1, None, "Regional Population >= 1"),
         ("--ventilated-los", int, 0, None, "Ventilated Length of Stay (days)"),
         ("--ventilated-rate", float, 0.0, 1.0, "Ventilated Rate: 0.0 - 1.0"),
     ):
@@ -110,7 +110,7 @@ def main():
         market_share=a.market_share,
         n_days=a.n_days,
         relative_contact_rate=a.relative_contact_rate,
-        susceptible=a.susceptible,
+        population=a.population,
 
         hospitalized=RateLos(a.hospitalized_rate, a.hospitalized_los),
         icu=RateLos(a.icu_rate, a.icu_los),
diff --git a/src/penn_chime/defaults.py b/src/penn_chime/defaults.py
index dd28427..9b60cd0 100644
--- a/src/penn_chime/defaults.py
+++ b/src/penn_chime/defaults.py
@@ -7,15 +7,12 @@ class Regions:
     """Arbitrary number of counties."""
 
     def __init__(self, **kwargs):
-        susceptible = 0
+        population = 0
         for key, value in kwargs.items():
             setattr(self, key, value)
-            susceptible += value
-        self._susceptible = susceptible
+            population += value
+        self.population = population
 
-    @property
-    def susceptible(self):
-        return self._susceptible
 
 
 class Constants:
@@ -55,4 +52,4 @@ class Constants:
         self.recovery_days = recovery_days
 
     def __repr__(self) -> str:
-        return f"Constants(susceptible_default: {self.region.susceptible}, known_infected: {self.known_infected})"
+        return f"Constants(population_default: {self.region.population}, known_infected: {self.known_infected})"
diff --git a/src/penn_chime/models.py b/src/penn_chime/models.py
index cc4858d..97fb33c 100644
--- a/src/penn_chime/models.py
+++ b/src/penn_chime/models.py
@@ -18,8 +18,7 @@ from .parameters import Parameters
 class SimSirModel:
 
     def __init__(self, p: Parameters) -> SimSirModel:
-        # TODO missing initial recovered value
-        susceptible = p.susceptible
+        # TODO missing initial non-zero 'recovered' value
         recovered = 0.0
         recovery_days = p.recovery_days
 
@@ -40,6 +39,8 @@ class SimSirModel:
             p.current_hospitalized / p.market_share / p.hospitalized.rate
         )
 
+        susceptible = p.population - infected
+
         detection_probability = (
             p.known_infected / infected if infected > 1.0e-7 else None
         )
diff --git a/src/penn_chime/parameters.py b/src/penn_chime/parameters.py
index 17b9722..7ea14da 100644
--- a/src/penn_chime/parameters.py
+++ b/src/penn_chime/parameters.py
@@ -17,7 +17,7 @@ class Parameters:
         doubling_time: float,
         known_infected: int,
         relative_contact_rate: float,
-        susceptible: int,
+        population: int,
 
         hospitalized: RateLos,
         icu: RateLos,
@@ -33,7 +33,7 @@ class Parameters:
         self.doubling_time = doubling_time
         self.known_infected = known_infected
         self.relative_contact_rate = relative_contact_rate
-        self.susceptible = susceptible
+        self.population = population
 
         self.hospitalized = hospitalized
         self.icu = icu
diff --git a/src/penn_chime/presentation.py b/src/penn_chime/presentation.py
index 7523295..8925561 100644
--- a/src/penn_chime/presentation.py
+++ b/src/penn_chime/presentation.py
@@ -41,7 +41,7 @@ def display_header(st, m, p):
 
     infected_population_warning_str = (
         """(Warning: The number of estimated infections is greater than the total regional population. Please verify the values entered in the sidebar.)"""
-        if m.infected > p.susceptible
+        if m.infected > p.population
         else ""
     )
 
@@ -92,7 +92,7 @@ and daily growth rate of **{daily_growth_t:.2f}%**.
             detection_prob_str=detection_prob_str,
             current_hosp=p.current_hospitalized,
             hosp_rate=p.hospitalized.rate,
-            S=p.susceptible,
+            S=p.population,
             market_share=p.market_share,
             recovery_days=p.recovery_days,
             r_naught=m.r_naught,
@@ -238,11 +238,11 @@ def display_sidebar(st, d: Constants) -> Parameters:
         step=1.0,
         format="%f",
     )
-    susceptible_input = NumberInputWrapper(
+    population_input = NumberInputWrapper(
         st_obj,
         "Regional Population",
         min_value=1,
-        value=d.region.susceptible,
+        value=d.region.population,
         step=100000,
         format="%i",
     )
@@ -261,7 +261,7 @@ def display_sidebar(st, d: Constants) -> Parameters:
 
     # Build in desired order
     st.sidebar.markdown("### Regional Parameters [ℹ]({docs_url}/what-is-chime/parameters)".format(docs_url=DOCS_URL))
-    susceptible = susceptible_input()
+    population = population_input()
     market_share = market_share_input()
     known_infected = known_infected_input()
     current_hospitalized = current_hospitalized_input()
@@ -298,7 +298,7 @@ def display_sidebar(st, d: Constants) -> Parameters:
         max_y_axis=max_y_axis,
         n_days=n_days,
         relative_contact_rate=relative_contact_rate / 100.0,
-        susceptible=susceptible,
+        population=population,
 
         hospitalized=RateLos(hospitalized_rate/ 100.0, hospitalized_los),
         icu=RateLos(icu_rate/ 100.0, icu_los),

diff --git a/tests/test_app.py b/tests/test_app.py
index f5dc5dc..696663e 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -20,7 +20,7 @@ PARAM = Parameters(
     known_infected=5000,
     market_share=0.05,
     relative_contact_rate=0.15,
-    susceptible=500000,
+    population=500000,
     hospitalized=RateLos(0.05, 7),
     icu=RateLos(0.02, 9),
     ventilated=RateLos(0.01, 10),
@@ -33,7 +33,7 @@ HALVING_PARAM = Parameters(
     known_infected=5000,
     market_share=0.05,
     relative_contact_rate=0.7,
-    susceptible=500000,
+    population=500000,
     hospitalized=RateLos(0.05, 7),
     icu=RateLos(0.02, 9),
     ventilated=RateLos(0.01, 10),
@@ -238,7 +238,7 @@ def test_model(model=MODEL, param=PARAM):
     # test the class-calculated attributes
     assert model.detection_probability == 0.125
     assert model.intrinsic_growth_rate == 0.12246204830937302
-    assert model.beta == 3.2961405355450555e-07
+    assert model.beta == 3.582761451679408e-07
     assert model.r_t == 2.307298374881539
     assert model.r_naught == 2.7144686763312222
     assert model.doubling_time_t == 7.764405988534983
@@ -251,16 +251,19 @@ def test_model(model=MODEL, param=PARAM):
     second = raw_df.iloc[1, :]
     last = raw_df.iloc[-1, :]
 
-    assert first.susceptible == 500000.0
+    assert first.susceptible + first.infected + first.recovered == param.population
+    assert last.susceptible + last.infected + last.recovered == param.population
+
+    assert first.susceptible == 460000.0
     assert round(second.infected, 0) == 43735
 
-    assert round(last.susceptible, 0) == 67202
-    assert round(raw_df.recovered[30], 0) == 224048
+    assert round(last.susceptible, 0) == 59497
+    assert round(raw_df.recovered[30], 0) == 216711
 
     assert list(model.dispositions_df.iloc[0, :]) == [0, 100.0, 40.0, 20.0]
-    assert [round(i, 0) for i in model.dispositions_df.iloc[60, :]] == [60, 1182.0, 473.0, 236.0]
+    assert [round(i, 0) for i in model.dispositions_df.iloc[60, :]] == [60, 1101.0, 441.0, 220.0]
 
-    # test that admissions are being properly calculated (thanks @PhilMiller)
+    # test that admissions are being properly calculated
     cumulative_admits = model.admits_df.cumsum()
     diff = cumulative_admits.hospitalized[1:-1] - (
         0.05 * 0.05 * (raw_df.infected[1:-1] + raw_df.recovered[1:-1]) - 100

Conflation of regional population with susceptible population is wrong with large infection count
The raw data shows a total of S+I+R that is larger than the user-provided regional population. This is because the number presumed initially infected based on hospitalization rate isn't subtracted from the population to compute the currently susceptible.
tests/test_app.py::test_sir tests/test_app.py::test_the_rest_of_header_shows_up tests/test_app.py::test_admitted_patients_chart tests/test_app.py::test_penn_logo_in_header tests/test_app.py::test_defaults_repr tests/test_app.py::test_new_admissions_chart tests/test_app.py::test_sim_sir tests/test_app.py::test_chart_descriptions tests/test_app.py::test_daily_growth_presentation tests/test_app.py::test_daily_growth_helper tests/test_app.py::test_mitigation_statement