SRT Time Calculator
Subtitles out of sync? Work out the exact delay, shift every cue by it, convert timing between frame rates or sync the whole file to two known points, then fix overlaps and numbering and download a clean SRT.
Subtitle delay calculator
Pick an early and a late cue and type the time each one should appear. Both offset and speed drift are corrected.
No timing change. Only the fixes below are applied.
Frames ↔ timecode
How to use the SRT Time Calculator
- Add your subtitles: paste them, upload or drop an .srt or .vtt file.
- Choose an adjustment: Shift offset, Frame rate or Two-point sync. Use the delay calculator if you don't know the offset yet.
- Tick the fixes you want, such as renumbering or fixing overlapping cues.
- Press Apply changes and check the result on the right.
- Press Download .srt to save the corrected subtitles, or Copy to paste them elsewhere.
The formulas behind subtitle timing
- Offset: new time = old time + offset. Offset = when the speech starts − when the subtitle appears.
- Frame-rate conversion: new time = old time × (subtitle fps ÷ video fps).
- Two-point sync: with cue A moving from a to A and cue B from b to B, the speed factor is k = (B − A) ÷ (b − a), the offset is A − k × a, and every time becomes k × t + offset.
Example: subtitles timed for 25 fps used with a 23.976 fps video. The factor is 25 ÷ 23.976 = 1.042709. A cue at 00:45:00,000 (2,700 s) moves to 2,700 × 1.042709 = 2,815.31 s = 00:46:55,314, almost two minutes later. That's why a frame-rate mismatch can't be fixed with a simple offset.
Frame-rate conversion factors
| Subtitles timed for | Video runs at | Multiply times by | Drift after 1 hour |
|---|---|---|---|
| 25 fps | 23.976 fps | 1.042709 | +2 min 33.8 s |
| 23.976 fps | 25 fps | 0.959040 | −2 min 27.5 s |
| 25 fps | 24 fps | 1.041667 | +2 min 30 s |
| 24 fps | 23.976 fps | 1.001001 | +3.6 s |
| 29.97 fps | 23.976 fps | 1.250000 | +15 min |
| 30 fps | 29.97 fps | 1.001001 | +3.6 s |
A 24 → 23.976 mismatch drifts only 3.6 seconds per hour, so the first half of a movie can look fine before the subtitles slowly fall behind. If the drift doesn't match any of these factors, use two-point sync instead.
Good subtitle timing
Professional style guides usually keep each subtitle on screen for at least about 1 second (often 5/6 s to 1.5 s) and at most about 7 seconds, with a reading speed of around 15 to 20 characters per second. Leave a small gap of 2 frames (about 80 ms at 25 fps) between consecutive cues so the viewer notices the change. The minimum duration and overlap fixes above help you meet these rules automatically.
Frequently asked questions
How do I calculate the subtitle delay?
Find a line in the video, note when its subtitle appears and when the speech actually starts, and type both times into the subtitle delay calculator. The offset is speech time minus subtitle time: if the subtitle shows at 1:02.000 and the speech starts at 1:03.250, the subtitles must be shifted by +1.250 seconds.
Positive or negative offset: which one do I need?
If the subtitles appear before the speech, they are early and need a positive offset to move them later. If they appear after the speech, use a negative offset to move them earlier. Cues that would move before 00:00:00 are clamped to zero.
When do I need frame-rate conversion?
When the subtitles drift further out of sync as the video plays, they were usually timed for a different frame rate. The classic case is subtitles made for a 25 fps PAL release used with a 23.976 fps version, or the other way around. Every timestamp is multiplied by the original frame rate divided by your video's frame rate.
What does two-point sync do?
You give the correct start time of an early cue and a late cue. The tool calculates a linear correction (a speed factor and an offset) that puts both cues exactly in place and stretches everything in between, which fixes drift and offset in one go.
Can it repair a broken SRT file?
Yes. It accepts dots instead of commas, missing or wrong cue numbers, Windows or Mac line endings and a byte order mark, and can sort cues, remove empty ones, fix overlaps and lengthen cues that flash by too quickly. The result is always a clean SRT with comma timestamps.
Are my subtitles uploaded?
No. The file is read and processed in your browser, and the download is created on your device.