The footage lifespan
How long dash cam footage lasts before it's overwritten
Dash cam footage lasts exactly as long as it takes loop recording to cycle back round and overwrite it. That length of time depends on your memory card's capacity, the resolution you record at and the bitrate your camera uses, not on which brand of camera you own. A clip only survives past that point if it has been locked, and even locked clips are eventually at risk once the card itself fills up.
The formula: how much footage a card actually holds
One calculation governs it: how many megabits your card can hold, divided by how many megabits your camera writes every second.
hours of footage = (card capacity in GB × 8,000) ÷ (bitrate in Mbps × 3,600)
A gigabyte holds 8,000 megabits. Divide the card's total megabits by the camera's bitrate in megabits per second to get seconds of footage, then divide by 3,600 to get hours.
Worked example. Say a camera records at 16 Mbps and the card is 64GB. That's 64 × 8,000, or 512,000 megabits on the card. Divide by 16 Mbps and you get 32,000 seconds, a little under 9 hours, before loop recording cycles back to the start. Change either number and the answer moves with it: a higher resolution or frame rate raises the bitrate, so the same card holds less time, and a bigger card at the same bitrate stretches further.
Manufacturers rarely publish a bitrate figure on the spec sheet, so the honest answer for your own setup is to go and check it. Play a recorded clip back on a computer and open its file properties: the Details tab on Windows, or Get Info on a Mac. That shows the actual bitrate and file size the camera used for that clip. Put that number, with your card's capacity, into the formula above, and you have a real figure rather than a guess.
What protects a clip from being overwritten
A clip only survives the loop if it has been locked. Most cameras lock a clip automatically when the impact sensor detects a knock, and most also give you a manual lock button to protect a clip on demand. A locked clip is generally moved into, or flagged within, a separate protected area of the card that ordinary loop recording is not allowed to write over.
What happens when the card fills with locked files
Locked files do not get recycled the way ordinary loop footage does, so every clip you lock, or the camera locks for you, takes a permanent bite out of the card until you remove it. Once the space set aside for locked files fills up, one of two things happens depending on the camera: it stops being able to lock anything new, or the unlocked loop area shrinks so far that recording itself starts to struggle.
This is the single most common real cause behind a dash cam that seems to have "stopped recording", covered in full on why your dash cam isn't recording everything.
Getting a clip off before it's lost
If you've just had an incident, locking the clip in camera is the first step, but copying it off the card entirely is the safer one: once it's on a phone or computer it no longer depends on the camera's own storage management at all. See how to view and get footage off a dash cam for the three ways to do that, in order of reliability.
Do this straight away rather than "later". If you plan to submit the footage to the police, there are practical deadlines for doing so, covered on can police prosecute with dash cam footage, which is exactly why speed matters here.
Questions
How long does dash cam footage last before it's overwritten?
It lasts until loop recording cycles back round to that segment, and that depends on your card's capacity, your recording resolution and your camera's bitrate, not on the camera's brand. Locking a clip protects it from that particular cycle, but a card full of locked files eventually runs out of room too.
What is the formula for how much footage a card holds?
Hours of footage equals the card's capacity in GB multiplied by 8,000, divided by the bitrate in Mbps multiplied by 3,600. Manufacturers rarely publish bitrate, so check a recorded clip's file properties on a computer to find your camera's real figure and put it into the formula yourself.
Does locking a clip stop it being deleted?
Yes, for as long as the card has room to store locked files separately from the loop. Once the space set aside for locked files fills up, the camera has to start either refusing new locks or running out of room altogether, depending on the model.
How do I check my dash cam's actual bitrate?
Play a recorded clip on a computer and open its file properties: the Details tab on Windows, or Get Info on a Mac. That shows the real bitrate and file size for your camera at the resolution you actually record at, rather than a marketing spec.
How quickly should I save footage after an incident?
Immediately. Loop recording has no way of knowing a clip matters unless you lock it or copy it off the card, and if you intend to submit footage to the police there are practical deadlines for doing so, so treat it as urgent rather than something to get to later.
Last reviewed 10 July 2026