diff --git a/src/index.ts b/src/index.ts
index 498abf1..ac1965f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -41,6 +41,14 @@ client.on(Events.InteractionCreate, (interaction) => {
   }
 });
 
+client.on(Events.EntitlementCreate, (entitlement) => {
+  void logger.log("info", `User ${entitlement.userId} has subscribed!`);
+});
+
+client.on(Events.EntitlementDelete, (entitlement) => {
+  void logger.log("info", `User ${entitlement.userId} has unsubscribed... :c`);
+});
+
 client.on(Events.ClientReady, () => {
   void logger.log("debug", "Bot is ready.");
 });
diff --git a/src/modules/alt.ts b/src/modules/alt.ts
index 93dd413..8bcaea2 100644
--- a/src/modules/alt.ts
+++ b/src/modules/alt.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 import type { ImageBlockParam } from "@anthropic-ai/sdk/resources/index.js";
 
@@ -109,4 +110,7 @@ export const alt = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "alt-text");
 };
diff --git a/src/modules/evaluate.ts b/src/modules/evaluate.ts
index 8ac2981..0605917 100644
--- a/src/modules/evaluate.ts
+++ b/src/modules/evaluate.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 
 /**
@@ -40,4 +41,7 @@ export const evaluate = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "evaluate");
 };
diff --git a/src/modules/mood.ts b/src/modules/mood.ts
index 42d2d17..3d0dbc3 100644
--- a/src/modules/mood.ts
+++ b/src/modules/mood.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 
 /**
@@ -41,4 +42,7 @@ export const mood = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "mood");
 };
diff --git a/src/modules/proofread.ts b/src/modules/proofread.ts
index 71f5af6..56dd70d 100644
--- a/src/modules/proofread.ts
+++ b/src/modules/proofread.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 
 /**
@@ -41,4 +42,7 @@ export const proofread = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "proofread");
 };
diff --git a/src/modules/query.ts b/src/modules/query.ts
index 68566d9..30c9df0 100644
--- a/src/modules/query.ts
+++ b/src/modules/query.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 
 /**
@@ -41,4 +42,7 @@ export const query = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "query");
 };
diff --git a/src/modules/summarise.ts b/src/modules/summarise.ts
index c58b84d..6b2d824 100644
--- a/src/modules/summarise.ts
+++ b/src/modules/summarise.ts
@@ -6,6 +6,7 @@
 import { MessageFlags, type ChatInputCommandInteraction } from "discord.js";
 import { personality } from "../config/personality.js";
 import { ai } from "../utils/ai.js";
+import { calculateCost } from "../utils/calculateCost.js";
 import { isSubscribed } from "../utils/isSubscribed.js";
 
 /**
@@ -41,4 +42,7 @@ export const summarise = async(
     response?.text
       ?? "I'm sorry, I don't have an answer for that. Please try again later.",
   );
+
+  const { usage } = messages;
+  await calculateCost(usage, interaction.user.username, "summarise");
 };
diff --git a/src/utils/calculateCost.ts b/src/utils/calculateCost.ts
new file mode 100644
index 0000000..2d90245
--- /dev/null
+++ b/src/utils/calculateCost.ts
@@ -0,0 +1,30 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+import { logger } from "./logger.js";
+import type { Usage } from "@anthropic-ai/sdk/resources/index.js";
+
+/**
+ * Calculates the cost of a command run by a user, and sends to
+ * our logging service.
+ * @param usage -- The usage payload from Anthropic.
+ * @param uuid -- The Discord ID of the user who ran the command.
+ * @param command -- The command that was run.
+ */
+export const calculateCost = async(
+  usage: Usage,
+  uuid: string,
+  command: string,
+): Promise<void> => {
+  const inputCost = usage.input_tokens * (3 / 1_000_000);
+  const outputCost = usage.output_tokens * (15 / 1_000_000);
+  const totalCost = inputCost + outputCost;
+  await logger.log(
+    "info",
+    `User ${uuid} ran \`${command}\` which accepted ${usage.input_tokens.toString()} and generated ${usage.output_tokens.toString()}.
+    
+    Total cost: ${totalCost.toLocaleString("en-GB", { currency: "USD", style: "currency" })}`,
+  );
+};