Under the CGST Act, 2017, the maximum GST rate that can be levied on all intra-state supplies of goods or services is 20%.

Explanation:
1. GST Rates:
- The Goods and Services Tax (GST) is a comprehensive indirect tax levied on the supply of goods and services in India.
- It is categorized into different rates based on the nature of goods or services and their essentiality to the economy.
- The GST rates are divided into four slabs: 5%, 12%, 18%, and 28%, with specific goods and services falling under each slab.

2. CGST Act, 2017:
- The Central Goods and Services Tax Act (CGST Act) is a legislation passed by the Indian Parliament to govern the levy and collection of GST on intra-state supplies.
- It is one of the key legislations that form the backbone of the GST regime in India.

3. Maximum GST Rate on Intra-state Supplies:
- Intra-state supplies refer to the transactions where the supply of goods or services and the consumption of those goods or services occur within the same state.
- The CGST Act, 2017 provides for a maximum GST rate that can be levied on such intra-state supplies.
- As per the Act, the maximum GST rate applicable to all intra-state supplies of goods or services is 20%.
- This means that any supply of goods or services within a state cannot attract a GST rate higher than 20%.

4. Impact and Flexibility:
- The maximum GST rate of 20% on intra-state supplies allows for flexibility in taxation while ensuring that the tax burden does not become excessive.
- It provides a cap on the maximum rate that can be charged, preventing any arbitrary increase in taxes.
- This helps in promoting business growth and maintaining a competitive environment.

In conclusion, the maximum GST rate that can be levied on all intra-state supplies of goods or services under the CGST Act, 2017 is 20%. This rate ensures that there is a limit on the tax burden imposed on intra-state transactions while maintaining a balance between revenue generation and business growth.