Backup Window Calculator
Find out how long a backup takes over your internet connection and whether it finishes inside your backup window.
Your data
A partial backup sends only the files that are new or edited since the last backup, which is how most backup software works day to day. If you are not sure how much changes, look at the size of last night's backup in your backup software, or the growth of your data over a week. A full backup sends everything every time. Compression and dedupe shrink what is actually sent, and the savings depend on the backup software and the kind of files.
Connection and window
Use the upload speed, not the download speed, because backups to the cloud or an offsite site go up. Cable and DSL upload is often much slower than download. If the backup should leave room for other traffic, pick a smaller share of the link. A window of 8 hours is roughly 10 PM to 6 AM. Use the speed converter to switch units.
Result
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Time is the data to send divided by the speed you can actually use, which is the upload speed times the efficiency times the share of the link. It assumes the backup software can keep the connection full and that the source and destination disks are fast enough. Sizes use 1 TB = 1,000 GB. Very small files, encryption, throttling by the provider and slow disks can all make real backups slower. A first full backup is often shipped on a drive or sent over several nights instead of one.