Backup upload time calculator
Plan your first backup using upload speed, data size, and the time your connection is available. No files are uploaded.
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How the estimate works
Minimum seconds = bytes × 8 ÷ (Mbps × 1,000,000)
Active upload time = minimum time ÷ usable fraction
Elapsed time = active time + gaps between daily upload windows
The schedule assumes one upload window at the same time every day and that the transfer starts at the beginning of the first window. If you need 12 active hours and have eight hours available daily, the result is 28 elapsed hours: eight uploading, 16 waiting, then four uploading. No waiting time is added after the transfer finishes.
GB is not GiB, and Mbps is not MB/s
GB and TB are decimal units: one billion and one trillion bytes. GiB and TiB use powers of two. A byte has eight bits, so 100 Mbps is at most 12.5 MB/s before overhead. Select the unit reported by the source of your data-size measurement.
Example: one terabyte at 20 Mbps
Uploading 1 TB at a continuous 20 Mbps takes at least 111.11 hours. With an illustrative 80% usable speed, it needs 138.89 active hours: about five days and 19 hours nonstop. Restricting the same transfer to eight-hour daily windows stretches elapsed time to about 17 days and three hours.
Why a real backup can take longer
File scanning, many small files, disk speed, encryption, connection interruptions, provider limits, and other household traffic can constrain progress. Compression or deduplication may reduce the bytes transferred. The calculator cannot predict these effects from a total file size alone.
Use observed sustained upload throughput where available. If your speed input already represents effective file-transfer throughput converted to Mbps, set usable share to 100% to avoid deducting overhead twice. A speed-test result is only a starting point.
Initial backup versus daily changes
For the first run, enter the amount you expect to transfer initially. For ongoing backups, calculate a representative day’s changed data separately. If daily changes require more active hours than your schedule allows, the upload backlog can grow even after the first backup finishes.
Compare upload speeds for a 1 TB backup.
Sources
Unit definitions: NIST binary prefixes. Backup timing context: Backblaze’s backup and restoration time frames. The worked examples and daily-window calculation are our own arithmetic. Methods and corrections.