diff --git a/README.md b/README.md
index de5b404..e0b904e 100644
--- a/README.md
+++ b/README.md
@@ -28,6 +28,22 @@ It's a single Python file with nothing extra to install.
 The timer keeps going (focus, break, focus, break...) until you press
 **Ctrl+C**. When you stop, it tells you how many focus sessions you finished.
 
+## Your focus log
+
+Every focus session you finish is saved to a log file called
+`pomodoro_log.csv` in your home folder. When you start the timer it shows
+how much you've already focused today, for example:
+
+```
+Today so far: 3 focus sessions, 1 hour 15 minutes in total.
+```
+
+and it shows the updated total again when you stop. Sessions you stop
+early with Ctrl+C aren't counted. The log is a plain spreadsheet file
+(one row per session, with the time it finished and how many minutes it
+was), so you can open it in Excel, Numbers or Google Sheets. Delete the file
+if you want to start fresh.
+
 ## Options
 
 You can change the times if you want:
@@ -38,6 +54,7 @@ You can change the times if you want:
 | `--break MINUTES` | Length of each break (default 5) | `--break 10` |
 | `--rounds N` | Stop after N focus sessions (default: keep going) | `--rounds 4` |
 | `--quiet` | Don't beep | `--quiet` |
+| `--log FILE` | Save the focus log somewhere else (default: `pomodoro_log.csv` in your home folder) | `--log work.csv` |
 
 For example, four rounds of 50 minutes work with 10 minute breaks:
 
diff --git a/pomodoro.py b/pomodoro.py
index 331e868..ddbcf15 100644
--- a/pomodoro.py
+++ b/pomodoro.py
@@ -5,15 +5,24 @@ Alternates between focus sessions (25 minutes by default) and breaks
 (5 minutes by default), showing a live countdown with a progress bar and
 ringing the terminal bell when each session ends.
 
+Every finished focus session is written to a small log file (a CSV file in
+your home folder by default), and today's total is shown when the timer
+starts.
+
 Uses only the Python standard library.
 """
 
 import argparse
+import csv
+import datetime
+import os
 import shutil
 import sys
 import time
 
 BELL = "\a"
+DEFAULT_LOG_FILE = os.path.join(os.path.expanduser("~"), "pomodoro_log.csv")
+LOG_HEADER = ["finished_at", "minutes"]
 
 
 def pick_bar_chars():
@@ -72,6 +81,59 @@ def run_session(label, minutes):
     sys.stdout.flush()
 
 
+def log_session(path, minutes):
+    """Add one finished focus session to the log file.
+
+    Returns True if it was saved. Problems writing the file are reported but
+    never stop the timer.
+    """
+    finished_at = datetime.datetime.now().replace(microsecond=0).isoformat(sep=" ")
+    try:
+        is_new = not os.path.exists(path) or os.path.getsize(path) == 0
+        with open(path, "a", newline="", encoding="utf-8") as f:
+            writer = csv.writer(f)
+            if is_new:
+                writer.writerow(LOG_HEADER)
+            writer.writerow([finished_at, f"{minutes:g}"])
+        return True
+    except OSError as e:
+        print(f"(Couldn't save this session to the log file {path}: {e.strerror or e})")
+        return False
+
+
+def today_totals(path, today=None):
+    """Return (number of sessions, total minutes) logged for today."""
+    today = (today or datetime.date.today()).isoformat()
+    count = 0
+    minutes = 0.0
+    try:
+        with open(path, newline="", encoding="utf-8") as f:
+            for row in csv.reader(f):
+                if len(row) < 2 or not row[0].startswith(today):
+                    continue
+                try:
+                    value = float(row[1])
+                except ValueError:
+                    continue
+                count += 1
+                minutes += value
+    except (OSError, UnicodeDecodeError):
+        pass
+    return count, minutes
+
+
+def describe_total(count, minutes):
+    sessions = "session" if count == 1 else "sessions"
+    total = int(round(minutes))
+    hours, mins = divmod(total, 60)
+    parts = []
+    if hours:
+        parts.append(f"{hours} hour" + ("" if hours == 1 else "s"))
+    if mins or not hours:
+        parts.append(f"{mins} minute" + ("" if mins == 1 else "s"))
+    return f"{count} focus {sessions}, {' '.join(parts)} in total"
+
+
 def ring(times):
     for i in range(times):
         sys.stdout.write(BELL)
@@ -122,6 +184,11 @@ def parse_args(argv=None):
         "-q", "--quiet", action="store_true",
         help="don't ring the terminal bell",
     )
+    parser.add_argument(
+        "-l", "--log", default=DEFAULT_LOG_FILE, metavar="FILE",
+        help="file where finished focus sessions are recorded "
+        "(default: %(default)s)",
+    )
     return parser.parse_args(argv)
 
 
@@ -135,6 +202,7 @@ def main(argv=None):
     focus_text = f"{args.focus:g} {plural(args.focus)}"
     break_text = f"{args.break_minutes:g} {plural(args.break_minutes)}"
     print(f"Pomodoro timer: {focus_text} focus, {break_text} break.")
+    print(f"Today so far: {describe_total(*today_totals(args.log))}.")
     print("Press Ctrl+C to stop.\n")
 
     completed = 0
@@ -145,6 +213,7 @@ def main(argv=None):
             print(f"Round {round_number}{suffix}")
             run_session("Focus", args.focus)
             completed += 1
+            log_session(args.log, args.focus)
             ring(ring_times)
 
             is_last = args.rounds and round_number >= args.rounds
@@ -161,6 +230,7 @@ def main(argv=None):
         print("\n\nStopped.")
 
     print(f"Focus sessions completed: {completed}. Nice work!")
+    print(f"Today's total: {describe_total(*today_totals(args.log))}.")
     return 0