diff --git a/cara/apps/calculator/model_generator.py b/cara/apps/calculator/model_generator.py
index 2e10b1f2..c6eeeeae 100644
--- a/cara/apps/calculator/model_generator.py
+++ b/cara/apps/calculator/model_generator.py
@@ -185,6 +185,10 @@ class FormData:
         return form_dict
 
     def validate(self):
+        # Validate number of infected <= number of total people
+        if self.infected_people > self.total_people:
+            raise ValueError('Number of infected people should be less than number of total people.')
+
         # Validate time intervals selected by user
         time_intervals = [
             ['exposed_start', 'exposed_finish'],
diff --git a/cara/tests/apps/calculator/test_model_generator.py b/cara/tests/apps/calculator/test_model_generator.py
index c1d1f2c2..534d038d 100644
--- a/cara/tests/apps/calculator/test_model_generator.py
+++ b/cara/tests/apps/calculator/test_model_generator.py
@@ -167,6 +167,13 @@ def test_ventilation_window_hepa(baseline_form: model_generator.FormData):
     assert ventilation == baseline_vent
 
 
+def test_infected_less_than_total_people(baseline_form: model_generator.FormData):
+    baseline_form.total_people = 10
+    baseline_form.infected_people = 11
+    with pytest.raises(ValueError, match='Number of infected people should be less than number of total people.'):
+        baseline_form.validate()
+
+
 def present_times(interval: models.Interval) -> models.BoundarySequence_t:
     assert isinstance(interval, models.SpecificInterval)
     return interval.present_times