This paper discusses the Union-to-State tax devolution in India during the years 2015 to 2024, which is constructed based on the proposals of the 14th Finance Commission and the 15th Finance Commission. It provides the vertical fiscal imbalance that persists in India, with the Union dominating the significant sources of revenue and the horizontal imbalance between the States with varying capabilities and needs. Based on secondary data in budget documents, Finance Commission reports, and Reserve Bank publications, the study runs both descriptive analysis and chi-square tests in determining the stability and equity of tax transfers. The research results indicate that tax devolution has been inequitable and fluctuating. Big States like Uttar Pradesh, Bihar and Madhya Pradesh got the maximum shares, with little going to the smaller States like Goa, Sikkim, and Mizoram. Arunachal Pradesh was a small state because of its strategic and geographical location. This was proven right by statistical tests, which means that State size had a significant effect on levels of allocation. The general trend also showed instability, whereby devolution reached its highest point in 2015-16 and was very low in other years, and this makes it hard for the States to plan their finances. Though the share of taxes to the States was raised by the 14th Finance Commission, subsequent changes in the 15th Finance Commission led to average transfers to many States, strengthening inequalities. The research concludes that the existing devolution system still favours the bigger States and proposes a more transparent, equitable and need-based system to reinforce fiscal decentralisation and create a balanced regional development.