diff --git a/calc.go b/calc.go
index 193e01f..e867d2f 100644
--- a/calc.go
+++ b/calc.go
@@ -18197,28 +18197,26 @@ func (fn *formulaFuncs) prepareXArgs(values, dates formulaArg) (valuesArg, dates
 			valuesArg = append(valuesArg, numArg.Number)
 			continue
 		}
-		err = newErrorFormulaArg(formulaErrorNUM, formulaErrorNUM)
+		err = newErrorFormulaArg(formulaErrorVALUE, formulaErrorVALUE)
 		return
 	}
 	if len(valuesArg) < 2 {
 		err = newErrorFormulaArg(formulaErrorNUM, formulaErrorNUM)
 		return
 	}
-	args, date := list.New(), 0.0
+	date := 0.0
 	for _, arg := range dates.ToList() {
-		args.Init()
-		args.PushBack(arg)
-		dateValue := fn.DATEVALUE(args)
-		if dateValue.Type != ArgNumber {
-			err = newErrorFormulaArg(formulaErrorNUM, formulaErrorNUM)
-			return
+		if arg.Type == ArgNumber {
+			datesArg = append(datesArg, arg.Number)
+			if arg.Number < date {
+				err = newErrorFormulaArg(formulaErrorVALUE, formulaErrorVALUE)
+				return
+			}
+			date = arg.Number
+			continue
 		}
-		if dateValue.Number < date {
-			err = newErrorFormulaArg(formulaErrorVALUE, formulaErrorVALUE)
-			return
-		}
-		datesArg = append(datesArg, dateValue.Number)
-		date = dateValue.Number
+		err = newErrorFormulaArg(formulaErrorVALUE, formulaErrorVALUE)
+		return
 	}
 	if len(valuesArg) != len(datesArg) {
 		err = newErrorFormulaArg(formulaErrorNUM, formulaErrorNUM)
diff --git a/calc_test.go b/calc_test.go
index a842a23..868533c 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -5562,13 +5562,13 @@ func TestCalcSUMIFSAndAVERAGEIFS(t *testing.T) {
 
 func TestCalcXIRR(t *testing.T) {
 	cellData := [][]interface{}{
-		{-100.00, "01/01/2016"},
-		{20.00, "04/01/2016"},
-		{40.00, "10/01/2016"},
-		{25.00, "02/01/2017"},
-		{8.00, "03/01/2017"},
-		{15.00, "06/01/2017"},
-		{-1e-10, "09/01/2017"},
+		{-100.00, 42370},
+		{20.00, 42461},
+		{40.00, 42644},
+		{25.00, 42767},
+		{8.00, 42795},
+		{15.00, 42887},
+		{-1e-10, 42979},
 	}
 	f := prepareCalcData(cellData)
 	formulaList := map[string]string{
@@ -5584,8 +5584,8 @@ func TestCalcXIRR(t *testing.T) {
 	calcError := map[string][]string{
 		"=XIRR()":                 {"#VALUE!", "XIRR requires 2 or 3 arguments"},
 		"=XIRR(A1:A4,B1:B4,-1)":   {"#VALUE!", "XIRR requires guess > -1"},
-		"=XIRR(\"\",B1:B4)":       {"#NUM!", "#NUM!"},
-		"=XIRR(A1:A4,\"\")":       {"#NUM!", "#NUM!"},
+		"=XIRR(\"\",B1:B4)":       {"#VALUE!", "#VALUE!"},
+		"=XIRR(A1:A4,\"\")":       {"#VALUE!", "#VALUE!"},
 		"=XIRR(A1:A4,B1:B4,\"\")": {"#NUM!", "#NUM!"},
 		"=XIRR(A2:A6,B2:B6)":      {"#NUM!", "#NUM!"},
 		"=XIRR(A2:A7,B2:B7)":      {"#NUM!", "#NUM!"},
@@ -5708,15 +5708,15 @@ func TestCalcXLOOKUP(t *testing.T) {
 func TestCalcXNPV(t *testing.T) {
 	cellData := [][]interface{}{
 		{nil, 0.05},
-		{"01/01/2016", -10000, nil},
-		{"02/01/2016", 2000},
-		{"05/01/2016", 2400},
-		{"07/01/2016", 2900},
-		{"11/01/2016", 3500},
-		{"01/01/2017", 4100},
+		{42370, -10000, nil},
+		{42401, 2000},
+		{42491, 2400},
+		{42552, 2900},
+		{42675, 3500},
+		{42736, 4100},
 		{},
-		{"02/01/2016"},
-		{"01/01/2016"},
+		{42401},
+		{42370},
 	}
 	f := prepareCalcData(cellData)
 	formulaList := map[string]string{
@@ -5732,9 +5732,9 @@ func TestCalcXNPV(t *testing.T) {
 		"=XNPV()":                 {"#VALUE!", "XNPV requires 3 arguments"},
 		"=XNPV(\"\",B2:B7,A2:A7)": {"#VALUE!", "strconv.ParseFloat: parsing \"\": invalid syntax"},
 		"=XNPV(0,B2:B7,A2:A7)":    {"#VALUE!", "XNPV requires rate > 0"},
-		"=XNPV(B1,\"\",A2:A7)":    {"#NUM!", "#NUM!"},
-		"=XNPV(B1,B2:B7,\"\")":    {"#NUM!", "#NUM!"},
-		"=XNPV(B1,B2:B7,C2:C7)":   {"#NUM!", "#NUM!"},
+		"=XNPV(B1,\"\",A2:A7)":    {"#VALUE!", "#VALUE!"},
+		"=XNPV(B1,B2:B7,\"\")":    {"#VALUE!", "#VALUE!"},
+		"=XNPV(B1,B2:B7,C2:C7)":   {"#VALUE!", "#VALUE!"},
 		"=XNPV(B1,B2,A2)":         {"#NUM!", "#NUM!"},
 		"=XNPV(B1,B2:B3,A2:A5)":   {"#NUM!", "#NUM!"},
 		"=XNPV(B1,B2:B3,A9:A10)":  {"#VALUE!", "#VALUE!"},