Not sure if it’s the same in the states (but I suspect it is), but in Canada, if your primary residence doubles in value and you sell it, you don’t have to pay

Not sure if it’s the same in the states (but I suspect it is), but in Canada, if your primary residence doubles in value and you sell it, you don’t have to pay tax on that investment income. However you would pay tax on all other investment income (real estate or stocks etc.). This is an exception to the tax rule and it’s a significant factor behind house prices (artificially low interest rates, and supply being other causes). It actually became a “smart” investment to over leverage for a primary residence because it’s a tax free investment that outperformed interest rates and other taxed investments.