diff --git a/execute.go b/execute.go
index 60b5742..8843f14 100644
--- a/execute.go
+++ b/execute.go
@@ -21,7 +21,7 @@ const modeIndexedIndirectX = 7
 const modeIndirectIndexedY = 8
 
 // https://www.masswerk.at/6502/6502_instruction_set.html
-
+// http://www.emulator101.com/reference/6502-reference.html
 func getWordInLine(line []uint8) uint16 {
 	return uint16(line[1]) + 0x100*uint16(line[2])
 }
@@ -41,20 +41,22 @@ func buildOPTransfer(regSrc int, regDst int) opFunc {
 	return func(s *state, line []uint8, opcode opcode) {
 		value := s.registers.getRegister(regSrc)
 		s.registers.setRegister(regDst, value)
-		// TODO: Update flags (N, Z)
+		if regDst != regSP {
+			s.registers.updateFlagZN(value)
+		}
 	}
 }
 
 func buildOpIncDecRegister(reg int, inc bool) opFunc {
 	return func(s *state, line []uint8, opcode opcode) {
-		value := s.registers.getRegister(reg) + 1
+		value := s.registers.getRegister(reg)
 		if inc {
 			value++
 		} else {
 			value--
 		}
 		s.registers.setRegister(reg, value)
-		// TODO: Update flags (N, Z) for all but TXS
+		s.registers.updateFlagZN(value)
 	}
 }
 
@@ -93,8 +95,7 @@ func buildOpLoad(addressMode int, regDst int) opFunc {
 		}
 
 		s.registers.setRegister(regDst, value)
-
-		// TODO: Update flags (N, Z)
+		s.registers.updateFlagZN(value)
 	}
 }
 
diff --git a/execute_test.go b/execute_test.go
index dde28e0..70ce222 100644
--- a/execute_test.go
+++ b/execute_test.go
@@ -12,6 +12,16 @@ func TestLoad(t *testing.T) {
 		t.Error("Error in LDA #")
 	}
 
+	executeLine(&s, []uint8{0xA9, 0x00})
+	if s.registers.getP() != flagZ {
+		t.Error("Error in flags for LDA $0")
+	}
+
+	executeLine(&s, []uint8{0xA9, 0xF0})
+	if s.registers.getP() != flagN {
+		t.Error("Error in flags for LDA $F0")
+	}
+
 	executeLine(&s, []uint8{0xA0, 0xFE})
 	if s.registers.getY() != 0xFE {
 		t.Error("Error in LDY #")
@@ -84,6 +94,9 @@ func TestTransfer(t *testing.T) {
 	if s.registers.getX() != 0xB0 {
 		t.Error("Error in TAX")
 	}
+	if s.registers.getP() != flagN {
+		t.Error("Error in TAX flags")
+	}
 
 	s.registers.setA(0xB1)
 	executeLine(&s, []uint8{0xA8})
@@ -114,3 +127,23 @@ func TestTransfer(t *testing.T) {
 		t.Error("Error in TYA")
 	}
 }
+
+func TestIncDec(t * testing.T) {
+	var s state
+
+	s.registers.setX(0x7E)
+	executeLine(&s, []uint8{0xE8})
+	if s.registers.getX() != 0x7F {
+		t.Errorf("Error in INX %v", s.registers.getX())
+	}
+
+	s.registers.setY(0xFC)
+	executeLine(&s, []uint8{0x88})
+	if s.registers.getY() != 0xFB {
+		t.Error("Error in DEY")
+	}
+	if s.registers.getP() != flagN {
+		t.Error("Error in DEY flags")
+	}
+
+}
diff --git a/registers.go b/registers.go
index 3780303..31aba75 100644
--- a/registers.go
+++ b/registers.go
@@ -9,6 +9,16 @@ const (
 	regPC = 6 // 2 bytes
 )
 
+const (
+	flagN uint8 = 1 << 7
+	flagV uint8 = 1 << 6
+	flagB uint8 = 1 << 4
+	flagD uint8 = 1 << 3
+	flagI uint8 = 1 << 2
+	flagZ uint8 = 1 << 1
+	flagC uint8 = 1 << 0
+)
+
 type registers struct {
 	data [8]uint8
 }
@@ -38,3 +48,28 @@ func (r *registers) setPC(v uint16) {
 	r.data[regPC] = uint8(v >> 8)
 	r.data[regPC+1] = uint8(v)
 }
+
+func (r *registers) getFlag(i uint8) bool {
+	return (r.data[regP] & i ) != 0
+}
+
+func (r *registers) setFlag(i uint8) {
+	r.data[regP] |= i
+}
+
+func (r *registers) clearFlag(i uint8) {
+	r.data[regP] &^= i
+}
+
+func (r *registers) updateFlag(i uint8, v bool) {
+	if v {
+		r.setFlag(i)
+	} else {
+		r.clearFlag(i)
+	}
+}
+
+func (r *registers) updateFlagZN(t uint8) {
+	r.updateFlag(flagZ, t == 0)
+	r.updateFlag(flagN, t >= (1<<7))
+}
diff --git a/registers_test.go b/registers_test.go
index 44d902d..45862cf 100644
--- a/registers_test.go
+++ b/registers_test.go
@@ -20,3 +20,50 @@ func TestRegPC(t *testing.T) {
 		t.Error("Error storing and loading PC")
 	}
 }
+
+func TestFlags(t *testing.T) {
+	var r registers
+	r.setP(0x23)
+	if r.getP() != 0x23 {
+		t.Error("Error storing and loading P")
+	}
+
+	r.setP(0)
+	r.setFlag(flagD)
+	if !r.getFlag(flagD) {
+		t.Error("Error setting and getting flag")
+	}
+
+	r.clearFlag(flagD)
+	if r.getFlag(flagD) {
+		t.Error("Error clearing flag")
+	}
+
+	r.updateFlag(flagD, true)
+	if !r.getFlag(flagD) {
+		t.Error("Error update flag to true")
+	}
+
+	r.updateFlag(flagD, false)
+	if r.getFlag(flagD) {
+		t.Error("Error updating flag to false")
+	}
+}
+
+func TestUpdateFlagZN(t *testing.T) {
+	var r registers
+	r.updateFlagZN(0)
+	if r.getP() != flagZ {
+		t.Error("Error update flags ZN with 0")
+	}
+
+	r.updateFlagZN(0x10)
+	if r.getP() != 0 {
+		t.Error("Error update flags ZN with 0x10")
+	}
+
+	r.updateFlagZN(0xF2)
+	if r.getP() != flagN {
+		t.Error("Error update flags ZN with 0xF2")
+	}
+}
\ No newline at end of file