Samsung S21 vs S25: Real World Performance, Camera, and Battery Tested After Four Years Apart

If your Galaxy S21 is still in your pocket right now, you're not alone. Samsung made that thing to last. It was a genuinely great phone in 2021, and for a lot of people, it still does the job. But with the Galaxy S25 landing at the same $799 / €899 launch price that the S21 debuted at four years ago, the obvious question is: how much has actually changed, and is the gap big enough to justify the jump?

To give you a grounded picture, this comparison draws on aggregated benchmark data, published battery tests from outlets including PhoneArena and Notebookcheck, camera analysis across multiple review publications, and Geekbench 6 results pulled directly from the benchmark browser. Where real-world performance is referenced, it's based on findings reported across independent testing rather than a single hands-on session. The goal is to tell you where Samsung actually moved the needle and where they've mostly reshuffled deck chairs.

Full Specs at a Glance

The Chipset Gap Is Larger Than You Think

This is where the generational jump is most dramatic, and I don't think it's talked about enough in the context of the S21. The S21 shipped with either the Snapdragon 888 or the Exynos 2100 depending on your region. Neither of those chips aged particularly gracefully. The Exynos 2100, which most European buyers got, was always the weaker of the two, and by 2025 it shows. Heavy apps take a noticeable extra beat to load, multitasking starts to stutter if you push the phone hard, and gaming at high settings causes the device to warm up uncomfortably fast.

The Snapdragon 8 Elite in the S25 posts a single-core Geekbench 6 score of around 2,883 and a multi-core score of around 9,518. The Exynos 2100, by comparison, sits at roughly 1,100 single-core and under 3,200 multi-core on the same benchmark. That's not a small gap. That's a different era.

In daily use scenarios reported across review publications, the S25 handles demanding workloads without hesitation. Titles like Genshin Impact at max settings, heavy multitasking, and video exports in Samsung's built-in editor all run noticeably smoother than on the S21. According to multiple reviewer accounts, the S21 manages these tasks too, but thermal throttling kicks in sooner under sustained load, and render times are meaningfully longer. If you're a power user, the S21 isn't going to keep pace anymore.

Samsung has also given the S25 12GB of RAM versus the S21's 8GB. That extra 4GB is what lets the S25 keep more apps suspended in the background without a hard reload. Based on aggregated user reports and reviewer testing, the difference is consistently noticeable during a normal workday of switching between a browser, messaging apps, music, and a camera. If you're a power user looking for that same level of performance in your desktop setup, our interactive PC Build Compatibility Checker can help you design a balanced rig that matches the S25's efficiency.

Display: Brighter Wins in the Real World

Both phones carry a 6.2-inch FHD+ AMOLED display with a 120Hz refresh rate, and on paper the gap looks smaller than it reportedly feels in practice. But here's what the spec sheet doesn't capture: the S25 pushes 2,600 nits at peak brightness, which is double the 1,300 nits found on the S21.

According to aggregated real-world assessments from review outlets, the S21 washes out noticeably in direct outdoor sunlight while the S25 stays readable without shielding the screen. That might sound minor, but for anyone who uses their phone outside regularly, it's the kind of upgrade that shows up every single day.

The S25 also uses an LTPO display panel and comes with thinner bezels that add up to a 5% increase in screen-to-body ratio relative to its 2021 counterpart. The S21 was never a bad looking phone, but next to the S25, those bezels look chunky in a way that wasn't obvious until the comparison.

Camera: More Megapixels Aren't the Whole Story

Here's where it's worth pushing back on the hype a little. Samsung's decision to go from a 12MP main sensor on the S21 to a 50MP sensor on the S25 sounds like a massive leap, and in some respects it is. But the 64MP telephoto lens on the S21 was genuinely good for its time, and Samsung replaced it with a 10MP shooter on the S25. A 10MP telephoto with modern processing versus a 64MP telephoto with four-year-old software. It's not a simple comparison.

The Galaxy S25 and Galaxy S25 Plus rely on a 50MP wide angle lens, a 12MP ultrawide angle lens and a 10MP telephoto one. The Galaxy S21 features a 16MP wide lens, a 64MP telephoto lens and a 12MP ultrawide lens. According to aggregated camera test data from multiple review publications, the S25 produces sharper daylight images with better natural color science. Where the S21 tends to over-saturate and oversharpen (classic Samsung), the S25 reportedly delivers a more controlled, more natural output.

In low light, the S25 wins decisively across published camera evaluations. Its larger sensor absorbs more light per pixel, and Samsung's night processing has come a long way since 2021. Independent testing consistently shows the S21 producing visible grain and blown highlights in dim indoor conditions while the S25 handles the same scenes with cleaner shadows and more accurate white balance.

The AI features on the S25 are genuinely useful in ways the S21 simply can't access anymore. The S25 comes with generative edits, instant slow-mo, best face (Samsung's take on Google's Best Take feature) and a new audio eraser. While Samsung has rolled out a few of these features to older Samsung Galaxy devices, the only things that have made their way back to the Galaxy S21 are Circle to Search and the ability to rewrite text messages using generative AI. If you rely on the camera for anything beyond point-and-shoot snapshots, the S25 is a meaningful step forward.

Battery Life: Same Capacity, Very Different Result

The numbers here are more interesting than they first appear. Both phones carry a 4,000mAh battery. Same size. But the efficiency difference between the Snapdragon 8 Elite and the old Exynos 2100 is stark.

PhoneArena's battery testing shows the S21 estimating around 4 hours 28 minutes of battery life, with about 7 hours 47 minutes of browsing. The S25 comes in at 7 hours 6 minutes of battery life estimate, with a browsing figure of 18 hours 29 minutes. That browsing number is particularly telling. According to aggregated data across multiple review outlets, the S25 consistently gets users through a full day with charge to spare, while the S21 regularly falls short by early evening for moderate-to-heavy users.

Charging speeds are identical on both phones. Both max out at 25W wired and 15W wireless. That's a broadly shared frustration with Samsung's lineup. Google's Pixel 9 charges at 27W, Apple's iPhone 16 Pro hits 27W MagSafe, and competitors like OnePlus and Xiaomi are clearing 65W to 100W. Samsung leaving charging speeds flat across four years while competitors have lapped them twice is hard to ignore.

Software and Long-Term Support: The Real Game Changer

The S21 launched with One UI 3.1 in 2021. Samsung promised four years of OS updates. That window has closed. The S21 tops out at Android 14, meaning you're no longer getting new Android features or, more importantly, security patches going forward.

The S25, by contrast, ships with Android 15 and Samsung has committed to seven years of OS updates. Seven. That takes the S25 to Android 22, which isn't something we can fully comprehend right now but means the phone you buy today is genuinely protected and supported until 2032. For anyone who keeps their phone for three to four years, that commitment changes the value calculation significantly.

If you care at all about security, especially for banking apps or work email, the S21's update window being closed is a legitimate reason to upgrade beyond benchmarks and cameras.

Should You Upgrade from the S21?

The S25 is a meaningfully better phone in almost every measurable dimension. The chip is dramatically faster, the display is noticeably brighter, battery life is considerably improved despite identical capacity, and the camera's low light performance is in a different league. But the honest answer to whether you should upgrade depends almost entirely on what your S21 is doing wrong right now.

If your S21 still runs smoothly, the battery gets you through most of your day, and you don't do much photography in challenging conditions, you can wait. Maybe wait for the Galaxy S26, which is already circulating in rumors for early 2026 and would give you an even better generational leap. But if your S21 is throttling on daily tasks, the battery is noticeably degraded after four years of charge cycles, or you're frustrated by apps that require the latest Android security patches, the S25 at $799 / €899 is a confident purchase. You're not just getting newer hardware. You're buying seven more years of relevant software.

For EU buyers, keep an eye on refurbished and open-box S25 units on platforms like Back Market, where you can regularly find them at €700 to €750, which is a strong deal for what you're getting.

For a deeper look at how Samsung's flagship performance holds up against Apple's competition, check out our Samsung Galaxy S26 Ultra vs. Apple iPhone 17 Pro Max comparison. And if you're interested in the latest foldables, our Motorola Razr vs Samsung Galaxy Z Flip comparison covers how Samsung handles the competition in that space.

For full spec verification, you can cross-reference the official Samsung Galaxy S25 specs on Samsung's site.

Verdict

The Samsung S25 wins this comparison cleanly. The Snapdragon 8 Elite chipset is a generational leap over both Snapdragon 888 and Exynos 2100 variants of the S21, the display nearly doubles the peak brightness where it counts most (outdoors), and battery efficiency is dramatically better despite the same 4,000mAh cell. The camera system isn't a raw megapixel win, but the real-world image quality in low light and the AI processing pipeline put it firmly ahead. The seven-year software commitment is the quiet, unsexy reason that seals the deal for anyone planning to keep their phone for more than two years.

Buy the Galaxy S25 if your S21 is struggling with daily performance, the battery doesn't last anymore, or you need continued security updates for work or banking. At $799 / €899 new, or ~€700 refurbished in Europe, it's a justified upgrade.

Stick with the S21 a bit longer only if it's still running reliably and you're planning to upgrade in 2026 when the Galaxy S26 series lands. The S21 isn't broken. It's just four years old.

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