In short
Three questions decide: how old is it, does it have an SSD, and how much memory does it have. A laptop up to about six years old with an SSD and 8 gigabytes becomes usable again with a clean-up, which takes an hour. One with an old hard drive is usually only worth it with a new SSD, around 100 EUR plus fitting. Older than eight years, under 8 gigabytes or no updates for Windows 11: buy new, because every euro put into the old device is lost.
First check what is inside
On Windows: Settings, System, About shows processor and memory. In Task Manager (Ctrl, Shift, Esc) under Performance, "Disk" tells you whether it is an SSD or an HDD. On a Mac: Apple menu, About This Mac. These three numbers decide everything else.
What a clean-up does and does not do
Clean-up means: prune startup programs (in Task Manager under Startup, switch off everything not needed), remove preinstalled adware and old antivirus leftovers, catch up on Windows updates, free up disk space, clear out browser extensions. On a device with an SSD this often brings back half the waiting time. "Optimiser" programs from the internet do nothing, they are usually the brake themselves.
What a clean-up does not cure: a mechanical hard drive. If the device grinds for three minutes after switching on and every program takes ten seconds to open, it is the hard drive, and no setting in the world changes that.
When an SSD saves the device
A laptop from 2018 to 2021 with an old hard drive and at least 8 gigabytes of memory becomes a different device with an SSD: start in 20 seconds instead of three minutes. The SSD costs around 60 to 100 EUR, plus fitting and moving the system. With soldered drives, as in many thin devices, this is not possible, and only buying new remains.
When buying new is cheaper
From about eight years, with 4 gigabytes of memory, or if the device cannot get Windows 11: Windows 10 has had no security updates since October 2025, and a device without updates no longer belongs anywhere near online banking. A new laptop for everyday use, e-mail and photos costs 450 to 700 EUR. Everything you put into the old device before that is then lost.
What you do not need: gaming graphics cards, 32 gigabytes of memory, the most expensive model on the shelf. What you need: an SSD, 16 gigabytes, a screen you can read well and a keyboard you like. Our purchase advice is free and independent, we sell nothing.