Samsung Galaxy S21 Ultra 5G vs Samsung Galaxy S25 Slim

Compare Samsung Galaxy S21 Ultra 5G vs Samsung Galaxy S25 Slim side by side: Exynos 2100 / Snapdragon 888 5G (5 nm) vs Qualcomm Snapdragon 8 Elite for Galaxy…

Samsung

Galaxy S25 Slim

$999

12categories won

4 categories tied · 21 scored in total · add a third phone

Information Gain

Which one wins?

MxMob Algorithmic Verdict

Samsung Galaxy S21 Ultra 5G takes the overall win

Overall Pick

The Samsung Galaxy S21 Ultra 5G claims the overall win over the Samsung Galaxy S25 Slim, delivering a stronger technical package across battery endurance and core hardware. For battery longevity and charging speed, the Galaxy S21 Ultra 5G takes the lead, while the Galaxy S25 Slim is the clear choice for demanding 3D gaming and heavy multitasking. Choose the Galaxy S21 Ultra 5G if you want the highest performance ceiling, or opt for the Galaxy S25 Slim if its lower retail price better fit your budget.

🔋 BatteryGalaxy S21 Ultra 5G

Galaxy S21 Ultra 5G wins on endurance with 5,000 mAh and 25W fast charging.

🎮 GamingGalaxy S25 Slim

Galaxy S25 Slim provides greater sustained gaming output with its Qualcomm Snapdragon 8 Elite for Galaxy and 16GB RAM.

📸 CameraGalaxy S21 Ultra 5G

Galaxy S21 Ultra 5G wins photography with 108MP main imaging and 10x dedicated optical zoom.

🏷️ ValueGalaxy S25 Slim

Galaxy S25 Slim wins on budget and value at $999 compared to $1199.

Category verdicts are computed algorithmically from verified technical specifications and hardware benchmarks. Rows where neither figure is objectively better — screen size preference, operating system choice, aesthetic build materials — are displayed for direct reference without scoring bias.

Galaxy S21 Ultra 5G vs Galaxy S25 Slim: specifications compared

Display

Display comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Screen size	6.8"	6.66"
Resolution	1440 x 3200Winner	1440 x 3120
Pixel density	516 ppi	516 ppi
Refresh rate	120 Hz	120 Hz
Peak brightness	1500 nits	3000 nitsWinner

Performance

Performance comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Chipset	Exynos 2100 / Snapdragon 888 5G (5 nm)	Qualcomm Snapdragon 8 Elite for Galaxy
Process node	5 nm	3 nmWinner
AnTuTu score	870,000	2,400,000Winner
Geekbench multi	3800	8900Winner
Maximum RAM	12 GB	16 GBWinner
Maximum storage	128GB	512GBWinner

Camera

Camera comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Main sensor	108 MPWinner	50 MP
Rear cameras	4Winner	2
Optical zoom	10x	—
Ultrawide	12 MP	12 MP
Selfie camera	40 MPWinner	16 MP
Max video	8K at 24fps / 4K at 60fps all cameras	8K at 30fps / 4K at 120fps

Battery and charging

Battery and charging comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Capacity	5,000 mAhWinner	4,400 mAh
Wired charging	25 W	45 WWinner
Wireless charging	15 W	15 W

Design

Design comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Weight	227 g	168 gWinner
Thickness	8.9 mm	6.6 mmWinner
Water resistance	IP68	IP68
Build	Aluminum frame, Gorilla Glass Victus front and back	Grade 5 Titanium frame, Gorilla Glass Armor 2 front, matte glass back

Software and support

Software and support comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
Operating system	Android 11	Android 15
OS updates	4 years	7 yearsWinner
Security updates	5 years	7 yearsWinner

Connectivity and value

Connectivity and value comparison between the Samsung Galaxy S21 Ultra 5G, Samsung Galaxy S25 Slim
Specification	Galaxy S21 Ultra 5G	Galaxy S25 Slim
5G	Yes	Yes
Wi-Fi	Wi-Fi 6E (802.11ax)	Wi-Fi 7 (802.11be, tri-band 2.4/5/6GHz, 320MHz bandwidth)
Storage expansion	None	None
3.5mm jack	No	No
Launch price	$1,199	$999Winner