The domination number of a graph G $G$, denoted γ
(
G
) $\gamma (G)$, is the minimum size of a dominating set of G $G$, and the independent domination number of G $G$, denoted i
(
G
) $i(G)$, is the minimum size of a dominating set of G $G$ that is also independent. Let k
≥
4 $k\ge 4$ be an integer. Generalizing a result on cubic graphs by Lam, Shiu, and Sun, we prove that i
(
G
)
≤
k
−
1
2
k
−
1
false|
V
(
G
)
false| $i(G)\le \frac{k-1}{2k-1}|V(G)|$ for a connected k $k$‐regular graph G $G$ that is not K
k
,
k ${K}_{k,k}$, which is tight for k
=
4 $k=4$. This answers a question by Goddard et al. in the affirmative. We also show that i
(
G
)
γ
(
G
)
≤
k
3
−
3
k
2
+
2
2
k
2
−
6
k
+
2 $\frac{i(G)}{\gamma (G)}\le \frac{{k}^{3}-3{k}^{2}+2}{2{k}^{2}-6k+2}$ for a connected k $k$‐regular graph G $G$ that is not K
k
,
k ${K}_{k,k}$, strengthening upon a result of Knor, Škrekovski, and Tepeh. In addition, we prove that a graph G $G$ with maximum degree at most 4 satisfies i
(
G
)
≤
5
9
false|
V
(
G
)
false| $i(G)\le \frac{5}{9}|V(G)|$, which is also tight.