Protected areas remain a key tool in the fight against biodiversity loss and have expanded rapidly in recent decades. However, protected areas are also increasingly experiencing downsizing events that reduce the total amount of area legally under protection. Here we explore how future predicted protected area expansion and downsizing (by 2045) will impact the ability for countries to meet representation and area-based protection targets, such as those set by the Convention on Biological Diversity. We found that predicted protected area downsizing will likely decrease habitat representation equality and mean area-based target (30% target) achievement by 50% and >80%, respectively, of the 36 countries analyzed across four scenarios (no protection, business as usual, random and optimal protection). Prioritizing protection of underrepresented ecoregions could offset these unfavorable outcomes, increasing representation equality, on average, by >60% and mean target achievement by >30%. We identify countries that are expected to decrease both representation equality and mean target achievement (~50% of countries across scenarios) with predicted downsizing. These countries need to pay particular attention to strategic protected area expansion and policies that prevent downsizing in parks with under-represented habitats. Finally, we identify cases where downsizing events improve protected area metrics, such as India and Nigeria, highlighting the complexities and potential trade-offs of protected area dynamics. A deeper understanding of the influence of protected area downsizing on conservation outcomes is urgently needed to ensure representative and adequate protected area networks.