Why is my upload speed so much slower than my download speed?

Most residential connections are deliberately asymmetric, meaning far more capacity is allocated to downloading than uploading. This is a design decision rather than a fault. Historically households consumed much more than they sent, and the underlying technologies for cable and telephone-line broadband allocate their frequency ranges accordingly.

The ratio can be dramatic. A connection offering very fast downloads may provide a small fraction of that upward, and that figure is what governs video calls, cloud backups, sending large files and hosting anything from home.

Fibre connections are often symmetric or much closer to it, which is one of the more meaningful practical differences when comparing services and is easy to overlook when comparing only the headline download figure.

There is a second effect that makes a slow upload feel worse than the number suggests. Because most protocols acknowledge received data, saturating your upload capacity delays those acknowledgements and can slow your downloads noticeably. A large backup running in the background can therefore degrade browsing even though the download capacity is untouched. Traffic shaping on the router, prioritising small acknowledgement packets, largely resolves this.

If your upload is slower than the figure you were sold rather than simply lower than your download, the usual causes are the same as any speed problem: the wireless link rather than the connection, an old or failing cable, or line quality issues that the provider can test remotely.

When it genuinely limits you, options are limited to changing the technology rather than the plan, since the asymmetry is a property of the underlying connection type.