Part vs whole
The whole is the base you measure against: the full budget, the whole sample, the old price. The part is what you compare to it. Swap them and you get a different answer: 300 of 2,000 is 15%, but 2,000 of 300 is 666.67%.
Over 100% is fine
If the part is larger than the whole the result exceeds 100%. Hitting 120% of a target means doing 1.2 times the target.
Examples
45 correct answers out of 60 is 75%. Spending 18,000 of a 40,000 budget is 45%. 27 out of 30 is 90%.