diff --git a/src/main.rs b/src/main.rs
index 33fd3fa..5d34b91 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -129,6 +129,10 @@ struct Args {
     /// Continue processing other inputs even if some fail; exit non-zero if any failed
     #[arg(long = "continue-on-error")]
     continue_on_error: bool,
+
+    /// Overwrite existing output files instead of appending a numeric suffix
+    #[arg(long = "force")]
+    force: bool,
 }
 
 #[derive(Debug, Deserialize)]
@@ -511,13 +515,13 @@ fn run() -> Result<()> {
                 // In merge+separate mode, always write merged output inside the provided directory
                 let base = outp.join(format!("{}_merged", polyscribe::date_prefix()));
                 let root = OutputRoot { items: merged_items.clone() };
-                write_outputs(&base, &root, &out_formats)?;
+                write_outputs(&base, &root, &out_formats, args.force)?;
             } else {
                 // For single merged file, ensure the parent dir exists
                 if let Some(parent) = outp.parent() { create_dir_all(parent).ok(); }
                 let base = outp.with_file_name(format!("{}_{}", polyscribe::date_prefix(), outp.file_name().and_then(|s| s.to_str()).unwrap_or("out")));
                 let root = OutputRoot { items: merged_items.clone() };
-                write_outputs(&base, &root, &out_formats)?;
+                write_outputs(&base, &root, &out_formats, args.force)?;
             }
         } else {
             // Print JSON to stdout
@@ -547,7 +551,7 @@ fn run() -> Result<()> {
                 let root = OutputRoot { items };
                 let stem = path.file_stem().and_then(|s| s.to_str()).unwrap_or("output");
                 let base = out_dir.join(format!("{}_{}", polyscribe::date_prefix(), stem));
-                write_outputs(&base, &root, &out_formats)?;
+                write_outputs(&base, &root, &out_formats, args.force)?;
             } else if is_audio_file(path) {
                 // Skip in tests
             }
diff --git a/src/output.rs b/src/output.rs
index 3f4420f..770cd44 100644
--- a/src/output.rs
+++ b/src/output.rs
@@ -1,6 +1,6 @@
 use std::fs::File;
 use std::io::Write;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 
 use anyhow::Context;
 
@@ -20,10 +20,41 @@ impl OutputFormats {
     }
 }
 
+fn any_target_exists(base: &Path, formats: &OutputFormats) -> bool {
+    (formats.json && base.with_extension("json").exists())
+        || (formats.toml && base.with_extension("toml").exists())
+        || (formats.srt && base.with_extension("srt").exists())
+}
+
+fn with_suffix(base: &Path, n: usize) -> PathBuf {
+    let parent = base.parent().unwrap_or_else(|| Path::new(""));
+    let name = base.file_name().and_then(|s| s.to_str()).unwrap_or("out");
+    parent.join(format!("{}_{}", name, n))
+}
+
+fn resolve_base(base: &Path, formats: &OutputFormats, force: bool) -> PathBuf {
+    if force {
+        return base.to_path_buf();
+    }
+    if !any_target_exists(base, formats) {
+        return base.to_path_buf();
+    }
+    let mut n = 1usize;
+    loop {
+        let candidate = with_suffix(base, n);
+        if !any_target_exists(&candidate, formats) {
+            return candidate;
+        }
+        n += 1;
+    }
+}
+
 /// Write outputs for the given base path (without extension).
 /// This will create files named `base.json`, `base.toml`, and `base.srt`
 /// according to the `formats` flags. JSON and TOML will always end with a trailing newline.
-pub fn write_outputs(base: &Path, root: &OutputRoot, formats: &OutputFormats) -> anyhow::Result<()> {
+pub fn write_outputs(base: &Path, root: &OutputRoot, formats: &OutputFormats, force: bool) -> anyhow::Result<()> {
+    let base = resolve_base(base, formats, force);
+
     if formats.json {
         let json_path = base.with_extension("json");
         let mut json_file = File::create(&json_path).with_context(|| {
@@ -70,7 +101,7 @@ mod tests {
         let items = vec![OutputEntry { id: 0, speaker: "Alice".to_string(), start: 0.0, end: 1.23, text: "Hello".to_string() }];
         let root = OutputRoot { items };
 
-        write_outputs(&base, &root, &OutputFormats::all()).unwrap();
+        write_outputs(&base, &root, &OutputFormats::all(), false).unwrap();
 
         let json_path = base.with_extension("json");
         let toml_path = base.with_extension("toml");
@@ -86,4 +117,33 @@ mod tests {
         assert!(json.ends_with('\n'), "json should end with newline");
         assert!(toml.ends_with('\n'), "toml should end with newline");
     }
+
+    #[test]
+    fn suffix_is_added_when_file_exists_unless_forced() {
+        let dir = tempfile::tempdir().unwrap();
+        let base = dir.path().join("run");
+
+        // Precreate a toml file for base to simulate existing output
+        let pre_path = base.with_extension("toml");
+        std::fs::create_dir_all(dir.path()).unwrap();
+        std::fs::write(&pre_path, b"existing\n").unwrap();
+
+        let items = vec![OutputEntry { id: 0, speaker: "A".to_string(), start: 0.0, end: 1.0, text: "Hi".to_string() }];
+        let root = OutputRoot { items };
+        let fmts = OutputFormats { json: false, toml: true, srt: false };
+
+        // Without force, should write to run_1.toml
+        write_outputs(&base, &root, &fmts, false).unwrap();
+        assert!(base.with_file_name("run_1").with_extension("toml").exists());
+
+        // If run_1.toml also exists, next should be run_2.toml
+        std::fs::write(base.with_file_name("run_1").with_extension("toml"), b"x\n").unwrap();
+        write_outputs(&base, &root, &fmts, false).unwrap();
+        assert!(base.with_file_name("run_2").with_extension("toml").exists());
+
+        // With force, should overwrite the base.toml
+        write_outputs(&base, &root, &fmts, true).unwrap();
+        let content = std::fs::read_to_string(pre_path).unwrap();
+        assert!(content.ends_with('\n'));
+    }
 }