diff --git a/core/src/main/kotlin/org/nwapw/abacus/number/NumberRangeBuilder.kt b/core/src/main/kotlin/org/nwapw/abacus/number/NumberRangeBuilder.kt
new file mode 100644
index 0000000..c0ed09c
--- /dev/null
+++ b/core/src/main/kotlin/org/nwapw/abacus/number/NumberRangeBuilder.kt
@@ -0,0 +1,24 @@
+package org.nwapw.abacus.number
+
+import org.nwapw.abacus.Abacus
+
+/**
+ * A utility class for creating [NumberRange] instances.
+ *
+ * Unlike a regular [ClosedRange], a NumberRange must have a third parameter,
+ * which is the [Abacus] instance that is used for promotion. However, the ".." operator
+ * is infix, and can only take two parameters. The solution is, instead of returning instances
+ * of NumberRange directly, to return a builder, which then provides a [with] infix function
+ * to attach it to an instance of Abacus.
+ * @property start the beginning of the range.
+ * @property endInclusive the end of the range.
+ */
+class NumberRangeBuilder(private val start: NumberInterface, private val endInclusive: NumberInterface) {
+
+    /**
+     * Generate a [NumberRange] with the given instance of [abacus].
+     * @return a new range with the given instance of Abacus.
+     */
+    infix fun with(abacus: Abacus) = NumberRange(abacus, start, endInclusive)
+
+}