diff --git a/maths/add_digits.py b/maths/add_digits.py
new file mode 100644
index 000000000000..90161f24a25a
--- /dev/null
+++ b/maths/add_digits.py
@@ -0,0 +1,31 @@
+def sum_of_digits(number: int) -> int:
+    """
+    Return the sum of decimal digits of a non-negative integer.
+
+    Parameters:
+        number (int): A non-negative integer whose digits will be summed.
+
+    Returns:
+        int: Sum of the decimal digits of `number`.
+
+    Examples:
+    >>> sum_of_digits(0)
+    0
+    >>> sum_of_digits(9)
+    9
+    >>> sum_of_digits(12345)
+    15
+    """
+    if number < 0:
+        raise ValueError("number must be a non-negative integer")
+
+    total = 0
+    while number:
+        total += number % 10
+        number //= 10
+    return total
+
+
+if __name__ == "__main__":
+    # simple demonstration
+    print(sum_of_digits(12345))  # expected 15