Backup Time & Window Calculator

Frequently Asked Questions

• What's the difference between full, incremental, and differential backups?

  A full backup copies everything, every file, every time. An incremental backup only copies files that changed since the last backup (full or incremental). A differential backup copies everything that changed since the last full backup, so it grows larger each day until the next full. Incremental is fastest for daily runs; differential is faster to restore because you only need the last full plus one differential set.
• Why does my first backup take so much longer than expected?

  The initial backup is always a full copy of your entire dataset, there's no shortcut. If you're backing up 4 TB over a 1GbE network, expect roughly 10-11 hours at real-world speeds. Over NBN upload, that same 4 TB could take 7 or more days. This is normal. After the seed, incremental backups typically finish in minutes because only changed data moves. Plan your first backup for a weekend or low-usage period.
• Does compression actually help with backup speed?

  It depends on your data. Compression reduces the volume of data transferred, roughly 30% less for typical mixed data (documents, databases, VMs). But it adds CPU load. If your NAS has a weak processor (e.g., a Realtek or older ARM chip), the compression overhead can offset the gains. Already-compressed data (MP4, JPEG, ZIP archives) won't shrink further. Test with your actual dataset to see the real impact on your hardware.
• How much does encryption slow down backups?

  Encryption typically adds a 10-15% speed penalty, this calculator uses 12%. On fast local connections, this is barely noticeable. On slow links where you're already bandwidth-constrained, it compounds the pain. Hardware-accelerated AES (available on most modern NAS CPUs from Intel and some ARM chips) reduces this penalty significantly. Check whether your NAS supports AES-NI in the specifications before disabling encryption to save time.
• Is cloud backup realistic on Australian NBN?

  For small to medium datasets (under 500 GB), yes, especially on NBN 50 or higher upload tiers. For multi-terabyte datasets, the initial seed over NBN is painful. A 4 TB dataset takes roughly 7-10 days at NBN 50 upload speeds. A common strategy is to seed the first full backup to a local drive, ship or carry it to the backup destination (or use a cloud provider's seed service), then let incremental sync handle daily changes over NBN. This is standard practice in Australian IT, not a workaround.
• What's a sensible backup window for home and small business?

  Most home users run backups overnight: 10 PM to 6 AM gives 8 hours. Small businesses with daytime operations typically use 8 PM to 6 AM (10 hours). The key is that the backup must finish before production use resumes, with at least 30-60 minutes of margin for overruns. If your backup can't finish in the window, switching to incremental backups is almost always the fix, they only move changed data, often completing in minutes even for large datasets.
• What about CGNAT and remote NAS backups?

  If your ISP uses Carrier-Grade NAT, common in Australia on NBN fixed wireless, satellite HFC, and some FTTP plans, you can't accept incoming connections, which breaks most self-hosted remote backup setups. Solutions include Tailscale or ZeroTier (overlay VPN that bypasses CGNAT), Synology QuickConnect, or cloud-based backup destinations that use outbound connections only (where you connect out to the cloud, not vice versa). This calculator estimates transfer time regardless of connectivity method: CGNAT determines which method you can use.
• How can I speed up my backups?

  The biggest wins, in order: switch from full to incremental (often 10-100× less data per run), enable compression if your data is compressible, upgrade the slowest link in the chain (usually the network), schedule backups during off-peak hours for less contention, and use deduplication if your backup tool supports it. Throwing faster disks at the problem only helps if the disk is actually the bottleneck, the slowest link indicator in this calculator tells you where to focus.