How long are macbooks supported?

Apple generally supports the hardware for five years before discontinuing hardware support, although some specific models may end up having a longer hardware support period because they were sold for longer than a year. Once Apple discontinues a specific model, the clock starts ticking for the five year hardware support window.

macOS & software support is somewhat tied to the hardware support. Once a new version of macOS is no longer officially supported on the hardware, then you will only receive security updates for another two years since Apple supports the current OS and supplies security updates for the previous two operating systems (some issues may not be patched in the last year of OS support). Some of the larger third party software vendors such as Microsoft only support their products on operating systems which are supported by Apple, so beware. Other third party software developers will provide support of older unsupported operating systems for many more years, while others may not provide updated versions of apps to work on unsupported operating systems, some developers will still allow the download of older versions of their apps.

Hello,

While MacBooks still get security updates and some macOS updates after they stop being eligible for macOS upgrades, you would only be one year of from potentially being left off of future versions of macOS.

Identify your MacBook model - Apple Support

"List of MacBook models

These models are organized by the year they were introduced, starting with the most recent. Models introduced in 2017 or later can run the latest version of macOS. For older models, the latest compatible operating system is noted."

Even further aware but may still be relevant to your decision is when your MacBook would fall into "obsolete" status for hardware support.

Obtaining service for your Apple product after an expired warranty - Apple Support

"Obtaining service for your Apple product after an expired warranty

Learn about your options for getting service and parts for Apple devices that are past their warranty period.

Owners of iPhone, iPad, iPod, Mac, or Apple TV products may obtain service and parts from Apple service providers, including Apple Retail Stores and Independent Repair Providers, for a minimum of 5 years from when Apple last distributed the product for sale.

Service and parts may be obtained for longer, as required by law or for up to 7 years, subject to parts availability. Additionally, Mac laptops may be eligible for an extended battery-only repair period for up to 10 years from when the product was last distributed for sale, subject to parts availability.

Apple discontinues hardware service for certain technologically-obsolete products. Your device is supported by ongoing OS updates and backed by a network of more than 5,000 Apple-certified repair locations that you can count on if something unexpected happens."

I hope this is helps.