diff --git a/src/lib/domain/project-health/project-health.test.ts b/src/lib/domain/project-health/project-health.test.ts
new file mode 100644
index 0000000000..fa678c3773
--- /dev/null
+++ b/src/lib/domain/project-health/project-health.test.ts
@@ -0,0 +1,203 @@
+import { subDays } from 'date-fns';
+import type { IFeatureType } from 'lib/types/stores/feature-type-store';
+import {
+    calculateProjectHealth,
+    calculateHealthRating,
+} from './project-health';
+
+const exampleFeatureTypes: IFeatureType[] = [
+    {
+        id: 'default',
+        name: 'Default',
+        description: '',
+        lifetimeDays: 30,
+    },
+    {
+        id: 'short-lived',
+        name: 'Short lived',
+        description: '',
+        lifetimeDays: 7,
+    },
+    {
+        id: 'non-expiring',
+        name: 'Long lived',
+        description: '',
+        lifetimeDays: null,
+    },
+];
+
+describe('calculateProjectHealth', () => {
+    it('works with empty features', () => {
+        expect(calculateProjectHealth([], exampleFeatureTypes)).toEqual({
+            activeCount: 0,
+            staleCount: 0,
+            potentiallyStaleCount: 0,
+        });
+    });
+
+    it('counts active toggles', () => {
+        const features = [{ stale: false }, {}];
+
+        expect(calculateProjectHealth(features, exampleFeatureTypes)).toEqual({
+            activeCount: 2,
+            staleCount: 0,
+            potentiallyStaleCount: 0,
+        });
+    });
+
+    it('counts stale toggles', () => {
+        const features = [{ stale: true }, { stale: false }, {}];
+
+        expect(calculateProjectHealth(features, exampleFeatureTypes)).toEqual({
+            activeCount: 2,
+            staleCount: 1,
+            potentiallyStaleCount: 0,
+        });
+    });
+
+    it('takes feature type into account when calculating potentially stale toggles', () => {
+        expect(
+            calculateProjectHealth(
+                [
+                    {
+                        stale: false,
+                        createdAt: subDays(Date.now(), 15),
+                        type: 'default',
+                    },
+                ],
+                exampleFeatureTypes,
+            ),
+        ).toEqual({
+            activeCount: 1,
+            staleCount: 0,
+            potentiallyStaleCount: 0,
+        });
+
+        expect(
+            calculateProjectHealth(
+                [
+                    {
+                        stale: false,
+                        createdAt: subDays(Date.now(), 31),
+                        type: 'default',
+                    },
+                ],
+                exampleFeatureTypes,
+            ),
+        ).toEqual({
+            activeCount: 1,
+            staleCount: 0,
+            potentiallyStaleCount: 1,
+        });
+
+        expect(
+            calculateProjectHealth(
+                [
+                    {
+                        stale: false,
+                        createdAt: subDays(Date.now(), 15),
+                        type: 'short-lived',
+                    },
+                ],
+                exampleFeatureTypes,
+            ),
+        ).toEqual({
+            activeCount: 1,
+            staleCount: 0,
+            potentiallyStaleCount: 1,
+        });
+    });
+
+    it("doesn't count stale toggles as potentially stale or stale as active", () => {
+        const features = [
+            {
+                stale: true,
+                createdAt: subDays(Date.now(), 31),
+                type: 'default',
+            },
+            {
+                stale: false,
+                createdAt: subDays(Date.now(), 31),
+                type: 'default',
+            },
+        ];
+
+        expect(calculateProjectHealth(features, exampleFeatureTypes)).toEqual({
+            activeCount: 1,
+            staleCount: 1,
+            potentiallyStaleCount: 1,
+        });
+    });
+
+    it('counts non-expiring types properly', () => {
+        const features = [
+            {
+                createdAt: subDays(Date.now(), 366),
+                type: 'non-expiring',
+            },
+            {
+                createdAt: subDays(Date.now(), 366),
+                type: 'default',
+            },
+        ];
+
+        expect(calculateProjectHealth(features, exampleFeatureTypes)).toEqual({
+            activeCount: 2,
+            staleCount: 0,
+            potentiallyStaleCount: 1,
+        });
+    });
+});
+
+describe('calculateHealthRating', () => {
+    it('works with empty feature toggles', () => {
+        expect(calculateHealthRating([], exampleFeatureTypes)).toEqual(100);
+    });
+
+    it('works with stale and active feature toggles', () => {
+        expect(
+            calculateHealthRating(
+                [{ stale: true }, { stale: true }],
+                exampleFeatureTypes,
+            ),
+        ).toEqual(0);
+        expect(
+            calculateHealthRating(
+                [{ stale: true }, { stale: false }],
+                exampleFeatureTypes,
+            ),
+        ).toEqual(50);
+        expect(
+            calculateHealthRating(
+                [{ stale: false }, { stale: true }, { stale: false }],
+                exampleFeatureTypes,
+            ),
+        ).toEqual(67);
+    });
+
+    it('counts potentially stale toggles', () => {
+        expect(
+            calculateHealthRating(
+                [
+                    { createdAt: subDays(Date.now(), 1), type: 'default' },
+                    {
+                        stale: true,
+                        createdAt: subDays(Date.now(), 1),
+                        type: 'default',
+                    },
+                    {
+                        stale: true,
+                        createdAt: subDays(Date.now(), 31),
+                        type: 'default',
+                    },
+                    {
+                        stale: false,
+                        createdAt: subDays(Date.now(), 31),
+                        type: 'default',
+                    },
+                ],
+                exampleFeatureTypes,
+            ),
+        ).toEqual(25);
+    });
+});
diff --git a/src/lib/domain/calculate-project-health/calculate-project-health.ts b/src/lib/domain/project-health/project-health.ts
similarity index 82%
rename from src/lib/domain/calculate-project-health/calculate-project-health.ts
rename to src/lib/domain/project-health/project-health.ts
index 36a00defd3..bd2299b889 100644
--- a/src/lib/domain/calculate-project-health/calculate-project-health.ts
+++ b/src/lib/domain/project-health/project-health.ts
@@ -2,12 +2,14 @@ import { hoursToMilliseconds } from 'date-fns';
 import type { IProjectHealthReport } from 'lib/types';
 import type { IFeatureType } from 'lib/types/stores/feature-type-store';
 
+type IPartialFeatures = Array<{
+    stale?: boolean;
+    createdAt?: Date;
+    type?: string;
+}>;
+
 const getPotentiallyStaleCount = (
-    features: Array<{
-        stale?: boolean;
-        createdAt?: Date;
-        type?: string;
-    }>,
+    features: IPartialFeatures,
     featureTypes: IFeatureType[],
 ) => {
     const today = new Date().valueOf();
@@ -20,17 +22,14 @@ const getPotentiallyStaleCount = (
 
         return (
             !feature.stale &&
+            featureTypeExpectedLifetime !== null &&
             diff >= featureTypeExpectedLifetime * hoursToMilliseconds(24)
         );
     }).length;
 };
 
 export const calculateProjectHealth = (
-    features: Array<{
-        stale?: boolean;
-        createdAt?: Date;
-        type?: string;
-    }>,
+    features: IPartialFeatures,
     featureTypes: IFeatureType[],
 ): Pick<
     IProjectHealthReport,
@@ -41,12 +40,8 @@ export const calculateProjectHealth = (
     staleCount: features.filter((f) => f.stale).length,
 });
 
-export const getHealthRating = (
-    features: Array<{
-        stale?: boolean;
-        createdAt?: Date;
-        type?: string;
-    }>,
+export const calculateHealthRating = (
+    features: IPartialFeatures,
     featureTypes: IFeatureType[],
 ): number => {
     const { potentiallyStaleCount, activeCount, staleCount } =
diff --git a/src/lib/services/project-health-service.ts b/src/lib/services/project-health-service.ts
index f28737774b..ede477bc85 100644
--- a/src/lib/services/project-health-service.ts
+++ b/src/lib/services/project-health-service.ts
@@ -11,8 +11,8 @@ import type { IProjectStore } from '../types/stores/project-store';
 import ProjectService from './project-service';
 import {
     calculateProjectHealth,
-    getHealthRating,
-} from '../domain/calculate-project-health/calculate-project-health';
+    calculateHealthRating,
+} from '../domain/project-health/project-health';
 
 export default class ProjectHealthService {
     private logger: Logger;
@@ -82,7 +82,7 @@ export default class ProjectHealthService {
             archived: false,
         });
 
-        return getHealthRating(toggles, this.featureTypes);
+        return calculateHealthRating(toggles, this.featureTypes);
     }
 
     async setHealthRating(): Promise<void> {