diff --git a/README.md b/README.md
index 7f8dc24..72fc7c8 100644
--- a/README.md
+++ b/README.md
@@ -127,24 +127,24 @@ $formats->get('decimal')->format(1000.1235); // 1 000,124
 $formats->get('currency')->format(1000.1235); // 1 000,12 Kč
 ```
 
-## Tax
+## Vat
 
 ```php
 use h4kuna\Format\Number;
 
-$tax = new Number\Tax(20);
-echo $tax->add(100); // 120
-echo $tax->deduct(120); // 100.0
+$tax = new Number\Vat(20);
+echo $tax->with(100); // 120
+echo $tax->without(120); // 100.0
 echo $tax->diff(120); // 20.0
 ```
 
-## Percent
+## Discount
 
 ```php
 use h4kuna\Format\Number;
 
-$percent = new Number\Percent(20);
-echo $percent->add(100); // 120.0
+$percent = new Number\Discount(20);
+echo $percent->with(100); // 120.0
 echo $percent->deduct(120); // 96.0
 echo $percent->diff(120); // 24.0
 ```
diff --git a/changelog.md b/changelog.md
index 9777a79..fcf4878 100644
--- a/changelog.md
+++ b/changelog.md
@@ -12,9 +12,9 @@ back compatibility with v5
 use h4kuna;
 class_alias(h4kuna\Format\Number\Formats::class, 'h4kuna\Number\Utils\Formats');
 class_alias(h4kuna\Format\Number\NumberFormat::class, 'h4kuna\Number\Format');
-class_alias(h4kuna\Format\Number\Percent::class, 'h4kuna\Number\Percent');
+class_alias(h4kuna\Format\Number\Discount::class, 'h4kuna\Number\Percent');
 class_alias(h4kuna\Format\Number\Round::class, 'h4kuna\Number\Utils\Round');
-class_alias(h4kuna\Format\Number\Tax::class, 'h4kuna\Number\Tax');
+class_alias(h4kuna\Format\Number\Vat::class, 'h4kuna\Number\Tax');
 class_alias(h4kuna\Format\Number\UnitValue::class, 'h4kuna\Number\Utils\UnitValue');
 
 // parameters
diff --git a/src/Number/Discount.php b/src/Number/Discount.php
new file mode 100644
index 0000000..6a411f6
--- /dev/null
+++ b/src/Number/Discount.php
@@ -0,0 +1,30 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Number;
+
+use h4kuna\Format\Utils;
+
+/**
+ * properties will become readonly
+ */
+final class Discount extends Percentage
+{
+
+	public function diff(float $number): float
+	{
+		return Utils\Percentage::diffDeduct($this->percentage, $number);
+	}
+
+
+	public function deduct(float $number): float
+	{
+		return Utils\Percentage::deduct($this->percentage, $number);
+	}
+
+
+	public function diffWith(float $number): float
+	{
+		return Utils\Percentage::diffWith($this->ratio, $number);
+	}
+
+}
diff --git a/src/Number/Percent.php b/src/Number/Percent.php
deleted file mode 100644
index 0fa2cb9..0000000
--- a/src/Number/Percent.php
+++ /dev/null
@@ -1,58 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace h4kuna\Format\Number;
-
-final class Percent
-{
-
-	private float $ratio;
-
-
-	public function __construct(private float $percent)
-	{
-		$this->ratio = ($percent / 100) + 1;
-	}
-
-
-	/**
-	 * @example 19.5% = float 19.5
-	 */
-	public function getPercent(): float
-	{
-		return $this->percent;
-	}
-
-
-	public function add(float $number): float
-	{
-		return $this->getRatio() * $number;
-	}
-
-
-	/**
-	 * @example 19.5% = float 1.195
-	 */
-	public function getRatio(): float
-	{
-		return $this->ratio;
-	}
-
-
-	public function deduct(float $number): float
-	{
-		return $number - $this->diff($number);
-	}
-
-
-	public function diff(float $number): float
-	{
-		return ($number / 100) * $this->percent;
-	}
-
-
-	public function __toString()
-	{
-		return (string) $this->percent;
-	}
-
-}
diff --git a/src/Number/Percentage.php b/src/Number/Percentage.php
new file mode 100644
index 0000000..3ef0990
--- /dev/null
+++ b/src/Number/Percentage.php
@@ -0,0 +1,35 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Number;
+
+use h4kuna\Format\Utils;
+
+abstract class Percentage
+{
+	public float $ratio;
+
+	public float $smallRatio;
+
+
+	public function __construct(public float $percentage)
+	{
+		$this->smallRatio = Utils\Percentage::smallRatio($this->percentage);
+		$this->ratio = Utils\Percentage::ratio($this->smallRatio);
+	}
+
+
+	public function with(float $number): float
+	{
+		return Utils\Percentage::with($this->ratio, $number);
+	}
+
+
+	abstract public function diff(float $number): float;
+
+
+	public function __toString()
+	{
+		return (string) $this->percentage;
+	}
+
+}
diff --git a/src/Number/Tax.php b/src/Number/Tax.php
deleted file mode 100644
index 5aecdfb..0000000
--- a/src/Number/Tax.php
+++ /dev/null
@@ -1,48 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace h4kuna\Format\Number;
-
-class Tax
-{
-	private Percent $vat;
-
-
-	public function __construct(int|float|Percent $vat)
-	{
-		if (!$vat instanceof Percent) {
-			$vat = new Percent($vat);
-		}
-		$this->vat = $vat;
-	}
-
-
-	public function getVat(): float
-	{
-		return $this->vat->getPercent();
-	}
-
-
-	public function add(float $number): float
-	{
-		return $this->vat->add($number);
-	}
-
-
-	public function diff(float $number): float
-	{
-		return $number - $this->deduct($number);
-	}
-
-
-	public function deduct(float $number): float
-	{
-		return $number / $this->vat->getRatio();
-	}
-
-
-	public function __toString()
-	{
-		return (string) $this->vat;
-	}
-
-}
diff --git a/src/Number/Vat.php b/src/Number/Vat.php
new file mode 100644
index 0000000..a31b703
--- /dev/null
+++ b/src/Number/Vat.php
@@ -0,0 +1,24 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Number;
+
+use h4kuna\Format\Utils;
+
+/**
+ * properties will become readonly
+ */
+class Vat extends Percentage
+{
+
+	public function diff(float $number): float
+	{
+		return Utils\Percentage::diffWithout($this->ratio, $number);
+	}
+
+
+	public function without(float $number): float
+	{
+		return Utils\Percentage::without($this->ratio, $number);
+	}
+
+}
diff --git a/src/Utils/Percentage.php b/src/Utils/Percentage.php
new file mode 100644
index 0000000..8e56603
--- /dev/null
+++ b/src/Utils/Percentage.php
@@ -0,0 +1,81 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Utils;
+
+/**
+ * Parameter $percentage is float represent percent, for example 17.5% -> 17.5
+ */
+final class Percentage
+{
+	/**
+	 * 17.5% -> 0.175
+	 */
+	public static function smallRatio(float $percentage): float
+	{
+		return $percentage / 100;
+	}
+
+
+	/**
+	 * 17.5% -> 1.175
+	 */
+	public static function ratio(float $smallRatio): float
+	{
+		return $smallRatio + 1.0;
+	}
+
+
+	/**
+	 * N + 17.5% -> N * 1.175
+	 */
+	public static function with(float $ratio, float $number): float
+	{
+		return $number * $ratio;
+	}
+
+
+	/**
+	 * N * 1.175 - N
+	 */
+	public static function diffWith(float $ratio, float $number): float
+	{
+		return self::with($ratio, $number) - $number;
+	}
+
+
+	/**
+	 * If you have price with percentage, and you need price without percentage.
+	 * N / 1.175
+	 */
+	public static function without(float $ratio, float $number): float
+	{
+		return $number / $ratio;
+	}
+
+
+	/**
+	 * N - (N / 1.175)
+	 */
+	public static function diffWithout(float $ratio, float $number): float
+	{
+		return $number - self::without($ratio, $number);
+	}
+
+
+	/**
+	 *  N - ((N * 17.5) / 100)
+	 */
+	public static function deduct(float $percentage, float $number): float
+	{
+		return $number - self::diffDeduct($percentage, $number);
+	}
+
+
+	/**
+	 * (N * 17.5) / 100
+	 */
+	public static function diffDeduct(float $percentage, float $number): float
+	{
+		return self::smallRatio($number * $percentage);
+	}
+}
diff --git a/tests/src/Number/DiscountTest.php b/tests/src/Number/DiscountTest.php
new file mode 100644
index 0000000..2c4b277
--- /dev/null
+++ b/tests/src/Number/DiscountTest.php
@@ -0,0 +1,32 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Tests\Number;
+
+use h4kuna\Format\Number\Discount;
+use h4kuna\Format\Tests\TestCase;
+use Tester\Assert;
+
+require __DIR__ . '/../../bootstrap.php';
+
+/**
+ * @testCase
+ */
+final class DiscountTest extends TestCase
+{
+
+	public function testDiscount(): void
+	{
+		$discount = new Discount(20);
+		Assert::same(120.0, $discount->with(100));
+		Assert::same(96.0, $discount->deduct(120));
+		Assert::same(24.0, $discount->diff(120));
+		Assert::same(20.0, $discount->diffWith(100));
+		Assert::same(20.0, $discount->percentage);
+		Assert::same(1.20, $discount->ratio);
+		Assert::same(0.20, $discount->smallRatio);
+		Assert::same('20', (string) $discount);
+	}
+
+}
+
+(new DiscountTest)->run();
diff --git a/tests/src/Number/PercentTest.php b/tests/src/Number/PercentTest.php
deleted file mode 100644
index faece25..0000000
--- a/tests/src/Number/PercentTest.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace h4kuna\Format\Tests\Number;
-
-use h4kuna\Format\Number\Percent;
-use h4kuna\Format\Tests\TestCase;
-use Tester\Assert;
-
-require __DIR__ . '/../../bootstrap.php';
-
-/**
- * @testCase
- */
-final class PercentTest extends TestCase
-{
-
-	public function testAdd(): void
-	{
-		$percent = new Percent(20);
-		Assert::same(120.0, $percent->add(100));
-	}
-
-
-	public function testDeduct(): void
-	{
-		$percent = new Percent(20);
-		Assert::same(96.0, $percent->deduct(120));
-	}
-
-
-	public function testDiff(): void
-	{
-		$percent = new Percent(20);
-		Assert::same(24.0, $percent->diff(120));
-		Assert::same(20.0, $percent->getPercent());
-	}
-
-}
-
-(new PercentTest)->run();
diff --git a/tests/src/Number/TaxTest.php b/tests/src/Number/TaxTest.php
deleted file mode 100644
index 533ca3d..0000000
--- a/tests/src/Number/TaxTest.php
+++ /dev/null
@@ -1,31 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace h4kuna\Format\Tests\Number;
-
-use h4kuna\Format\Number\Percent;
-use h4kuna\Format\Number\Tax;
-use h4kuna\Format\Tests\TestCase;
-use Tester\Assert;
-
-require __DIR__ . '/../../bootstrap.php';
-
-/**
- * @testCase
- */
-final class TaxTest extends TestCase
-{
-
-	public function testApi(): void
-	{
-		$tax = new Tax(20);
-		Assert::same(120.0, $tax->add(100));
-		Assert::same(100.0, $tax->deduct(120));
-		Assert::same(20.0, $tax->diff(120));
-		Assert::same(20.0, $tax->getVat());
-
-		Assert::same('20', (string) new Tax(new Percent(20)));
-	}
-
-}
-
-(new TaxTest)->run();
diff --git a/tests/src/Number/VatTest.php b/tests/src/Number/VatTest.php
new file mode 100644
index 0000000..d4e6708
--- /dev/null
+++ b/tests/src/Number/VatTest.php
@@ -0,0 +1,31 @@
+<?php declare(strict_types=1);
+
+namespace h4kuna\Format\Tests\Number;
+
+use h4kuna\Format\Number\Vat;
+use h4kuna\Format\Tests\TestCase;
+use Tester\Assert;
+
+require __DIR__ . '/../../bootstrap.php';
+
+/**
+ * @testCase
+ */
+final class VatTest extends TestCase
+{
+
+	public function testVat(): void
+	{
+		$vat = new Vat(20);
+		Assert::same(120.0, $vat->with(100));
+		Assert::same(100.0, $vat->without(120));
+		Assert::same(20.0, $vat->diff(120));
+		Assert::same(20.0, $vat->percentage);
+		Assert::same(1.20, $vat->ratio);
+		Assert::same(0.20, $vat->smallRatio);
+		Assert::same('20', (string) $vat);
+	}
+
+}
+
+(new VatTest)->run();