If Immanuel Kant states that we always have to act according to maxims of which we can at the same time will that they become a Universal law, how much does his conception differ from rule-utilism? In this summarized form there seems to be not difference: both principles order a certain way of acting without looking at the consequences per act. I here want to address this question, and argue why there is a difference.
Central in Kant’s ethics is the Categorical Imperative, a universal principle that applies to all reasonable beings. “Act only according to that maxim whereby you can, at the same time, will that it should become a universal law”, it states. If I can not wish a maxim to be a universal law applying to all reasonable being, it cannot be moral. It is, according to Kant, the only moral obligation, because all other thinkable imperatives serve a goal, and are therefore hypothetical imperatives. As long as an act is not done from the principle of duty, it has no moral worth, even when it brings happiness to you and to the other.
Utilitarianism (utilism in short) defends the so-called greatest happiness principle, which says that the right thing to do is the act that brings as much happiness as possible to as many as possible people. This almost per definition requires the use of rules, because calculating for each act what the possible consequences are is theoretically and practically impossible. Utilism knows two main conceptions on how to deal with these rules. Act-utilism says that these rules may be broken when this causes more happiness in a specific situation, rule-utilism states that one has to accept a set of rules that one is not allowed to break, even if the exception would bring more happiness about. The fact that a number of rule-utilitarians uses sub-rules that make exceptions possible indirectly is left out of consideration here, because with these sub-rules, the distinction between act- and rule-utilism blurs so much that it would make answering the question impossible.
To the question whether there is a difference between the conceptions of Kant and rule-utilism I surely can say “yes, there is.” In short, the two seem similar because both give strict rules for moral behavior, but in essence they differ strongly.
This difference lies in the fact that rule-utilism gives rules to block the possibility of bizarre exceptions. As an act-utilitarian it would not at all be problematic to cheat on your wife if that produced more overall happiness. Richard Brandt, among others, gives this as an argument against act-utilism. Although the categorical imperative does not allow exceptions in a similar way, rule-utilism gives rules with a goal in mind, where the categorical imperative is characterized by its being a goal in itself. Because rule-utilism in the end judges the morality of a set of rules (not of the rules in themselves), it is a consequentialist (also teleological) ethical theory; a theory that states that the outcomes of actions determine the moral worth. Kant’s ethical theory morally judges actions on basis of their motivations, and therefore of a fundamentally different kind, a deontological: an ethical theory based on rules, that looks at the motivated action instead of only the consequence. The rule-utilitarian thus assumes that morality is a means to general happiness, whereas Kant states that morality exists in itself, has no external purpose. It is the expressing of the free will of the person. In short: rule-utilism says that happiness is the greatest good, Kant says the good will is.
Stephen Darwall formulates the underlying normative difference as follows: the rule-utilitarian believes that together we are all responsible for everyone’s happiness, where Kant states that together we are all responsible for the conditions that are necessary for supplying everyone in what they need for living their (moral) lives.
A last difference is the following: a formulation of the categorical imperative that Kant names is that you must always treat people as ends, never as means.  Utilism puts everything in the service of the greater happiness, through which humanity (man-hood) automatically becomes a means.
So once again, yes, Kant’s view differs widely from utilism’s. Kant’s ethical theory is first of all a deontological, not a teleological. The set of moral rules of rule-utilism is given to promote a greater good, the categorical imperative has morality as a goal in itself. Then there are some differences in, for example, how the two treat acts concerning humanity (man-hood) and the conception of the greatest good. More than enough to separate the two.
 Subjective principle for acting
 Kant, Immanuel (1997) Fundering van de Metafysica van de Zeden. Amsterdam: Boom – p. 74
 Mill, John Stuart (1998) On liberty and other essays. Oxford: Oxford University Press – p. 457
 Brandt, Richard B. (1991) Philosophical Ethics: an Introduction to Moral Philosophy. New York: McGraw Hill – p. 152
 Darwall, Stephen (1997) Philosophical Ethics. Oxford: Westview Press – p.168
 O’Neill, Onora in Singer, Peter (1993) A Companion to Ethics. Oxford: Blackwell – p. 178-179