The repeating cycle of a repeating decimal for a rational number depends on the denominator after it has been simplified. For a denominator of 7, the length of the repeating cycle can be determined by finding the order of 10 modulo 7.
When you divide by 7, you can see that 10^1 (which is 10) mod 7 gives a remainder of 3, 10^2 gives a remainder of 2, 10^3 gives a remainder of 6, 10^4 gives a remainder of 4, and 10^5 gives a remainder of 5, while 10^6 gives a remainder of 1. This means that the order is 6, suggesting that the repeating decimal can have a cycle of up to 6 digits long.
Thus, the answer is: up to six digits long.