This paper examines the role of weight in stress assignment in the Portuguese lexicon, and proposes a probabilistic approach to stress. I show that weight effects are gradient, and weaken monotonically as we move away from the right edge of the word. Such effects depend on the position of a syllable in the word, as well as on the number of segments the syllable contains. The probabilistic model proposed in this paper is based on a single predictor, namely weight, and yields more accurate results than a categorical analysis, where weight is treated as binary. Finally, I discuss implications for the grammar of Portuguese.