Head to head
Samsung Galaxy S25vsSamsung Galaxy S21
The short answer
Choose the Galaxy S25 for peak brightness, video playback time and Geekbench 6 CPU score. The Galaxy S21 wins no row by a gap you’d notice. The Galaxy S21 is £30 cheaper at UK RRP (£769 against £799). The Galaxy S21’s security updates ended in February 2026; the Galaxy S25 gets them until January 2032.
- Released
- 2025-02-03endoflife.date, retrieved 2026-08-20
- Price
- £799Samsung Newsroom UK — Galaxy S25 series, retrieved 2026-08-20
- Security updates until
- 2032-01-31Samsung UK spec API — Galaxy S25, retrieved 2026-09-22
- Released
- 2021-01-29endoflife.date, retrieved 2026-08-20
- Price
- £769Samsung Newsroom UK — Galaxy S21 5G and S21+ 5G, retrieved 2026-08-20
- Security updates until
- 2026-02-21endoflife.date — Samsung mobile, retrieved 2026-09-06
3 wins for Galaxy S250 wins for Galaxy S211 gap borderline1 difference you won’t notice£30 apart at RRP
Verdict: Galaxy S25 ahead on 3 rows, Galaxy S21 on none
On the makers’ figures and the named third-party sources, the Galaxy S25 wins on peak brightness (2,600 nits against 1,300 nits, both from GSMArena), claimed video playback (29 h against 20 h) and Geekbench 6 (CPU, multi-core) (8,599 against 2,973, both from Geekbench Browser). One gap is borderline, a difference most people would not notice: RAM (12 GB against 8 GB) for the Galaxy S25. The difference in weight is below the threshold you would notice. Both state the same display size, refresh rate, storage (base), battery capacity, fast charging and wireless charging. The other 36 rows have no threshold or no direction to judge by, so nobody wins them.
True to scale
Outlines from each maker’s published dimensions, drawn to scale. Corner rounding is our drawing convention, not a measurement.
Specifications
A win is marked only where the figures can be ranked and the gap is one you could notice. A row the site has no threshold for says whether the two differ, and that it is not ranking them. = marks the same figure on both, ≠ not ranked a difference with no ranking. Every figure carries its source.
Body
Display
Platform
Memory
Camera
Battery
Connectivity
Benchmarks
4 attributes neither phone has a sourced figure for
Typical brightness · HDR peak brightness · OS versions supported · Google Mobile Services. Rows appear as sources are cited — a gap in our data, not a statement about either phone.
Questions
Is the Galaxy S25 better than the Galaxy S21?
On the figures, the Galaxy S25 is ahead wherever there is a gap you’d notice: peak brightness, 2,600 nits against 1,300 nits (both GSMArena), claimed video playback, 29 h against 20 h (both Samsung UK) and Geekbench 6 (CPU, multi-core), 8,599 against 2,973 (both Geekbench Browser). The Galaxy S21 wins no row by such a gap. That is a count of rows, not an overall score.
Which has the better battery?
The Galaxy S25, by a gap you’d notice: claimed video playback, 29 h against 20 h (both Samsung UK). Both state 4,000 mAh for battery capacity (Samsung Newsroom UK).
Which is lighter?
The Galaxy S25 is lighter on paper, but not by a gap you’d notice: weight, 162 g against 169 g (both Samsung Newsroom UK).
Which has the brighter screen?
The Galaxy S25, by a gap you’d notice: peak brightness, 2,600 nits against 1,300 nits (both GSMArena).
Which gets updates for longer?
The Galaxy S21’s security updates ended in February 2026; the Galaxy S25 gets them until January 2032. Sources: dates from Samsung UK spec API and endoflife.date.
Which is cheaper?
The Galaxy S21 is £30 cheaper at UK RRP (£769 against £799). Prices from Galaxy S25: Samsung Newsroom UK; Galaxy S21: Samsung Newsroom UK.
Other comparisons
The pairs a buyer of either phone would also weigh. Any two phones in the catalogue can be compared from the chooser.