CCTV Retention Days Calculator – Estimate DVR/NVR Recording Days Easily

CCTV Retention Days Calculator

More Tools: Online Tools for CCTV Security Systems


When we install CCTV cameras in our home, shop, or office, one common question comes to mind:

“How many days will my CCTV system keep recording?”

This is very important, because if an incident happens after a week or even a month, you should still be able to go back and check the footage. For this reason, we use a tool called the CCTV Retention Days Calculator.

This calculator helps you to estimate the number of days your DVR/NVR will store recordings on your hard disk, based on camera quality, recording hours, compression method, and HDD size.

In this guide, we will understand everything about CCTV retention days in simple language, and how you can calculate it easily.

What is CCTV Retention Days?

CCTV Retention Days means the number of days your CCTV system can keep video footage before it starts overwriting old data.

For example:

  • If your CCTV shows 15 days retention, it means footage older than 15 days will get deleted automatically and replaced with new recordings.
  • If your retention is 30 days, you can go back and check the last one month’s video.

The retention period depends on:

  1. Hard Disk size (HDD or NVR storage capacity)
  2. Number of cameras
  3. Resolution (720p, 1080p, 2K, 4K)
  4. FPS (frames per second)
  5. Compression type (H.264 / H.265)
  6. Bitrate type (CBR / VBR)
  7. Recording hours per day (24×7 or motion-based recording)

Why CCTV Retention Days Matter?

Retention days are not just a number. They play a big role in security planning:

  1. Legal Requirements – In some industries like banks, hotels, and corporate offices, government rules demand minimum 30 to 90 days of CCTV storage.
  2. Evidence Collection – If any theft, accident, or dispute happens, you may need old video as proof.
  3. Cost Planning – Hard disks are expensive. If you know your retention days, you can decide whether to buy 1TB, 2TB, or 4TB storage.
  4. Future Expansion – If you plan to add more cameras later, you can calculate in advance how much extra storage you will require.

How CCTV Retention Days Calculator Works

The CCTV Retention Days Calculator is a simple but powerful tool. It works on this formula:

Retention Days = (Total HDD Storage in bits) ÷ (Total storage used by all cameras per day)

The calculator takes following inputs:

  • Number of Cameras – how many cameras are connected to DVR/NVR.
  • Recording Hours per Day – 24 hours if continuous recording, less if only during working hours.
  • Resolution – 720p, 1080p, 2K, 4K etc. Higher resolution = bigger file size.
  • Frame Rate (FPS) – higher FPS means smoother video but more storage required.
  • Encoding Type – H.264 or H.265. H.265 compresses better and saves 30–40% storage.
  • Bitrate Type – CBR (constant bitrate) or VBR (variable bitrate). VBR usually saves storage.
  • HDD Size – how big your hard disk is, in GB or TB.

Using these factors, the calculator tells you how many days your hard disk will last before it starts overwriting old data.

Example 1 – 4TB HDD, 8 Cameras

  • Cameras: 8
  • Resolution: 1080p
  • FPS: 20
  • Encoding: H.265
  • Hours per day: 24
  • Bitrate type: VBR
  • HDD size: 4TB

Estimated Retention: 20–25 days

Example 2 – 2TB HDD, 4 Cameras

  • Cameras: 4
  • Resolution: 720p
  • FPS: 15
  • Encoding: H.264
  • Hours per day: 12 (only working hours)
  • HDD size: 2TB

Estimated Retention: 30+ days

Factors Affecting CCTV Retention

  1. Number of Cameras
    More cameras = more video data = less retention days.
  2. Resolution
    • 720p requires less space.
    • 1080p requires 2–3 times more.
    • 4K requires 8–10 times more storage.
  3. Frame Rate (FPS)
    • 10–15 FPS is enough for normal security.
    • 25–30 FPS is used where smooth video is needed.
  4. Encoding
    • H.265 is much better than H.264.
    • Same HDD can give 30% more retention if H.265 is used.
  5. Bitrate Type
    • CBR (Constant) = same bitrate always.
    • VBR (Variable) = bitrate adjusts as per motion, saves storage.
  6. Recording Hours
    • 24×7 recording fills HDD fast.
    • Motion-based recording saves a lot of space.
  7. Scene Complexity
    • Busy areas (traffic, shops) use more bitrate.
    • Simple areas (store room, corridor) use less bitrate.

Benefits of CCTV Retention Days Calculator

  • Quick estimation – no manual math needed.
  • Avoid overspending – you don’t buy unnecessarily large HDD.
  • Compliance ready – you can plan storage for 30, 60, or 90 days as required.
  • Easy for everyone – shopkeepers, housing societies, offices, even home users can use it.

How to Increase Retention Days

If you want your CCTV to record for longer days without buying a new hard disk, here are some tips:

  1. Choose bigger HDD if budget allows – best long-term solution.
  2. Use H.265 compression – saves 30–40% space compared to H.264.
  3. Lower FPS – 12–15 FPS is enough for most security needs.
  4. Enable VBR – Variable bitrate uses less space when scene is still.
  5. Reduce resolution if not needed – for small shops, 720p or 1080p is fine. 4K is only required in very specific cases.
  6. Use motion recording – record only when there is activity.

Conclusion

A CCTV Retention Days Calculator is a must-have tool for anyone installing CCTV. Whether you are a small shop owner, a housing society, or a big company, it helps you plan storage smartly.

Instead of guessing “how many days my CCTV will record”, you can now calculate it in seconds. This saves cost, avoids problems, and makes sure your security system is reliable.

Next time you buy or upgrade a CCTV system, don’t forget to use the retention days calculator. It will clearly show whether your hard disk will last 7 days, 15 days, 30 days, or even more.