diff --git a/README.md b/README.md
index 28a1ed5..b078218 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ ToDo List:
 - [X] add unit tests
 - [X] allow to set variables
 - [X] read line comments
-- [ ] add modulus operator '%'
+- [X] add modulus operator '%'
 - [ ] add support for multiple characters operators
 - [ ] add inclusive operators like '!=', '>=', '<='
 - [ ] add input_number() std function
diff --git a/examples/sandbox.ltor b/examples/sandbox.ltor
new file mode 100644
index 0000000..ba642e2
--- /dev/null
+++ b/examples/sandbox.ltor
@@ -0,0 +1,2 @@
+# test modulus operator
+print_number(20.2 % 10)
diff --git a/src/evaluator.h b/src/evaluator.h
index 6748bf8..40a8424 100644
--- a/src/evaluator.h
+++ b/src/evaluator.h
@@ -2,7 +2,7 @@
 #ifndef EVALUATOR_H_
 #define EVALUATOR_H_
 
-#define EVALUATOR_DEBUG_LEVEL 1
+#define EVALUATOR_DEBUG_LEVEL 0
 
 int evaluate(struct StateContainer* state, char* inputStr, int* resultPtr, unsigned char* typePtr);
 
diff --git a/src/operate.c b/src/operate.c
index 309841b..b3ee816 100644
--- a/src/operate.c
+++ b/src/operate.c
@@ -8,6 +8,7 @@ int is_operator(char candidate) {
     return (
         candidate == '*' ||
         candidate == '/' ||
+        candidate == '%' ||
         candidate == '+' ||
         candidate == '-' ||
         candidate == '^' ||
@@ -81,6 +82,8 @@ int operate(
             res = a*b;
         } else if (operator == '/') {
             res = a/b;
+        } else if (operator == '%') {
+            res = m_float_modulus(a, b);
         } else if (operator == '^') {
             res = m_float_pow(a, b);
         } else if (operator == '=') {
@@ -109,6 +112,8 @@ int operate(
             res = aRepr*bRepr;
         } else if (operator == '^') {
             res = integer_pow(aRepr, bRepr);
+        } else if (operator == '%') {
+            res = (aRepr % bRepr);
         } else if (operator == '=') {
             res = (int) (aRepr == bRepr);
         } else if (operator == '<') {
diff --git a/src/utils.c b/src/utils.c
index 9a73776..9c9a5d9 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -84,6 +84,22 @@ float m_float_pow(float base, int exponent)
     return r;
 }
 
+float m_float_modulus(float a, float b)
+{
+    // find the remainder
+    float t = a;
+    float res = 0;
+    int i = 0;
+    while (i < 1000) {
+        t = t - b;
+        if (t < 0) {
+            return t+b;
+        }
+        i++;
+    }
+    return -1;
+}
+
 int m_factorial(int x)
 {
     if (x == 0 || x == 1) {
diff --git a/src/utils.h b/src/utils.h
index e8134ee..10cd57b 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -20,6 +20,8 @@ int integer_pow(int base, int exponent);
 
 int float_almost_equal(float a, float b);
 
+float m_float_modulus(float a, float mod);
+
 int m_factorial(int x);
 
 float m_float_pow(float base, int exponent);
diff --git a/tests/test.c b/tests/test.c
index eb0ac15..eb907c4 100644
--- a/tests/test.c
+++ b/tests/test.c
@@ -8,9 +8,9 @@
 int main()
 {
     printf("== UNIT TESTS == \n");
+    test_utils();
     test_var_store();
     test_stack();
-    test_utils();
     test_evaluation();
     test_line_processing();
 }
diff --git a/tests/test_evaluation.c b/tests/test_evaluation.c
index 8a8ae3f..bd0bbfb 100644
--- a/tests/test_evaluation.c
+++ b/tests/test_evaluation.c
@@ -133,4 +133,12 @@ void test_evaluation()
     evaluate(state, "5 > 0", &resVal, &resType);
     assert(resType == TYPE_INT);
     assert(1 == resVal);
+
+    evaluate(state, "5 % 10", &resVal, &resType);
+    assert(resType == TYPE_INT);
+    assert(5 == resVal);
+
+    evaluate(state, "5.3 % 10", &resVal, &resType);
+    assert(resType == TYPE_FLOAT);
+    assert(float_almost_equal(5.3, get_float_from_int_rep(resVal)));
 }
diff --git a/tests/test_utils.c b/tests/test_utils.c
index 7653637..fa7ab7c 100644
--- a/tests/test_utils.c
+++ b/tests/test_utils.c
@@ -39,6 +39,9 @@ void test_utils()
     assert(m_factorial(3) == 6);
     assert(m_factorial(4) == 2*3*4);
 
+    assert(float_almost_equal(2.22, m_float_modulus(2.22, 10)));
+    assert(float_almost_equal(28.619, m_float_modulus(200.22, 34.32)));
+
     assert(float_almost_equal(2.7182, m_exp(1.0)));
     assert(float_almost_equal(1, m_exp(0)));