“Attaining a mildly surprising DxOMark score of 86 points, the Nikon D3400 sensor is one of the best-performing sensors in the current lineup, despite being an entry-level model. It modestly surpasses the current mid-range D5500 and practically equals the D7200 in the overall scores, albeit falling behind the latter model in terms of Landscape (dynamic range at base ISO value) and Low-Light scores.”
Here are some comparison charts (Nikon D3400 compared with several different DSLRs):
From DxOMark Conclusion:
“As an entry-level APS-C model, the Nikon D3400 is difficult to beat in terms of sensor performance. Nikon has tweaked the sensor to the same level as the pricier D5500. However, except for the SnapBridge connectivity option, the D3400 is very close to that of the older and cheaper D3300, in terms of features and controls. While the bump in image quality is welcome, it’s not as though the D3300 was underperforming in any way, at least when compared with its rivals. But packaged with a new AF-P type kit lens that promises improved AF in live view, the D3400 is a step in the right direction.”
You can read the full review at DxOMark.