A 5 GB file "should" take 7 minutes on a 100 Mbps connection. So why is your progress bar predicting an hour? Slow transfers almost always come down to one of seven causes — and most are fixable in minutes once you know which one you're fighting. Work down this list in order.
1. Your upload speed isn't your download speed
The number your ISP advertises is usually download. Home connections are often asymmetric — 200 Mbps down, 20 Mbps up. When you're sending, your upload is the ceiling. Run a speed test and look at the upload figure; if it's 20 Mbps, a 5 GB send takes ~35 minutes no matter what tool you use. Fix: nothing beats physics, but see #2–#5 to reach the ceiling, and consider a fiber/upload-symmetric plan if you send professionally.
2. Wi-Fi is quietly eating half your speed
Wi-Fi adds retransmissions, interference, and distance loss — commonly costing 30–60% of throughput, more through walls. Fix: plug in ethernet for big transfers. No single change matters more. If cable is impossible, use the 5 GHz band and get close to the router.
3. Something else is using the pipe
Cloud backups (OneDrive, iCloud, Backblaze), game updates, and someone streaming 4K in the next room all share your upload. A background photo backup can consume nearly all of it. Fix: pause sync clients and downloads on both ends during the transfer.
4. The service itself is throttling you
Store-and-forward services shape traffic: free tiers get deprioritized, big files get queued, and busy hours slow everyone. That's a business model, not a network problem. Fix: use a route with no middleman to throttle — a direct P2P transfer runs at whatever your two connections support, since there's no server tier in between (how that works).
5. You're paying for two trips instead of one
Upload-to-server-then-download doubles total transfer time — your recipient can't finish until both legs complete. Fix: one-hop transfer. Your upload is their download, cutting elapsed time roughly in half (the math).
6. Thousands of small files instead of one big one
Per-file overhead is real: 10,000 small files transfer far slower than one archive of the same total size. Fix: zip folders before sending (folder guide).
7. The other side is the bottleneck
A transfer runs at the speed of the slower participant. If your upload is 500 Mbps but your recipient's hotel Wi-Fi downloads at 10 Mbps, that's the pace. Fix: ask the other side to check #2 and #3 too; schedule big sends when they're on a decent connection.
Quick diagnostic checklist
- Speed test on both ends — note upload (sender) and download (receiver).
- Ethernet on at least the sending machine.
- Pause backups/sync/streams on both ends.
- One zipped archive, not loose files.
- Use a direct, unthrottled route.
Expected result: a transfer running at ~90% of the slower side's honest speed. If you're far below that after all five steps, the connection itself (ISP congestion, VPN overhead) is the remaining suspect — test without VPN, and at a different hour.
FAQ
Why do transfers slow down at night? Evening ISP congestion — the whole neighborhood is streaming. Late-night and early-morning transfers often run measurably faster.
Does a VPN slow transfers? Usually yes (encryption overhead plus a detour through the VPN server). For non-sensitive transfers, turn it off; note that direct P2P transfers are already end-to-end encrypted without a VPN.
Is USB faster than online transfer? Not necessarily — cheap flash drives write at 10–30 MB/s (80–240 Mbps), and you pay that cost twice. A decent connection with a direct transfer beats it (comparison).
Put the checklist to work: start a full-speed transfer and watch what your connection can actually do.