Chop the cranberries to a medium dice (or larger if you prefer).
Combine the chopped cranberries, sugar (or sweetener) and water in a small saucepan.
Bring to a boil on medium heat. Lower heat and simmer to about 12 minutes until the mixture is thickened and jam like. You can place a saucer in the freezer and drop ¼ teaspoon on to the dish to check the gel, but this probably isn’t needed since cranberry jam is much less exacting than other jams.
Pour into a lidded jar or other covered container, cover and place in the refrigerator to finish thickening.
Notes
The listed calorie count is for 1/8 of the recipe, about 2 Tablespoons, made with sugar. If made with allulose sweetener, the calorie count would be about 6 for the same quantity.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.