diff --git a/backup.ts b/backup.ts
index 493a854..64d6d6c 100755
--- a/backup.ts
+++ b/backup.ts
@@ -2,7 +2,12 @@
 
 import * as hex from "https://deno.land/std@0.219.0/encoding/hex.ts";
 import * as fs from "https://deno.land/std@0.219.0/fs/mod.ts";
-import { Command } from "https://deno.land/x/cliffy@v1.0.0-rc.3/command/mod.ts";
+import {
+  ArgumentValue,
+  Command,
+  Type,
+  ValidationError,
+} from "https://deno.land/x/cliffy@v1.0.0-rc.3/command/mod.ts";
 
 function command(name: string, ...args: string[]): Promise<Deno.CommandOutput> {
   return new Deno.Command(name, { args }).output();
@@ -12,8 +17,34 @@ function print(encoded: Uint8Array): void {
   console.log(new TextDecoder().decode(encoded));
 }
 
+class KeepType extends Type<string> {
+  private readonly units = ["h", "d", "w", "m", "y"];
+
+  public parse({ label, name, value }: ArgumentValue): string {
+    const [end, ...rest] = value.split("").reverse();
+    const start = rest.reverse().join("");
+
+    if (!this.units.includes(end)) {
+      throw new ValidationError(
+        `${label} "${name}" has an invalid unit. Allowed values are: ${
+          this.units.join(", ")
+        }`,
+      );
+    }
+
+    const num = Number.parseInt(start, 10);
+    if (Number.isNaN(num)) {
+      throw new ValidationError(`${label} "${name}" is invalid.`);
+    }
+
+    const unit = end.replace("h", "H");
+    return `${num}${unit}`;
+  }
+}
+
 const cli = new Command()
   .name("backup")
+  .type("keep", new KeepType())
   .option("-v --verbose", "Enable verbose logging")
   .option(
     "--no-init",
@@ -23,13 +54,17 @@ const cli = new Command()
     required: true,
   })
   .option("-R --repo <path:file>", "Path to borg repo", { required: true })
-  .option("--rclone-remote <remote:string>", "Rclone remote name")
-  .option("--rclone-root <root:string>", "Rclone remote root directory", {
-    default: ".",
+  .option("--no-prune", "Disable automatic archive pruning")
+  .option("-K --keep <value:keep>", "Timeframe to keep backups for (eg: 7d)", {
+    required: true,
   })
   .option("-S --sync", "Sync repo using rclone", {
     depends: ["rclone-remote", "rclone-root"],
   })
+  .option("--rclone-remote <remote:string>", "Rclone remote name")
+  .option("--rclone-root <root:string>", "Rclone remote root directory", {
+    default: ".",
+  })
   .arguments("<...PATHS>")
   .action(async (args, ...paths) => {
     const borg = (...args: string[]) => command("borg", ...args);
@@ -46,11 +81,14 @@ const cli = new Command()
       Deno.exit(1);
     }
 
+    // TODO: Dry-run
     const {
       verbose,
       init,
       name,
       repo,
+      prune,
+      keep,
       sync,
     } = args;
 
@@ -104,7 +142,25 @@ const cli = new Command()
 
     if (verbose) print(resp.stderr);
 
-    // TODO: Automatic prune
+    if (prune) {
+      const resp = await borg(
+        "prune",
+        repo,
+        "--stats",
+        "--keep-last=1",
+        `--keep-within=${keep}`,
+      );
+
+      if (!resp.success) {
+        console.log("failed to prune backups");
+        if (verbose) print(resp.stderr);
+        Deno.exit(1);
+      }
+
+      if (verbose) print(resp.stderr);
+
+      // TODO: Detect borg 1.2.x and compact
+    }
 
     if (sync) {
       const { rcloneRoot, rcloneRemote } = args;