diff --git a/core/commonMain/src/ArgumentValues.kt b/core/commonMain/src/ArgumentValues.kt
index 81a1ac4..b57442a 100644
--- a/core/commonMain/src/ArgumentValues.kt
+++ b/core/commonMain/src/ArgumentValues.kt
@@ -75,7 +75,7 @@ internal abstract class ParsingValue<T: Any, TResult: Any>(val descriptor: Descr
      */
     fun addDefaultValue() {
         if (descriptor.defaultValueSet) {
-            parsedValue = descriptor.defaultValue!!
+            parsedValue = descriptor.defaultValue!!.value
             valueOrigin = ArgParser.ValueOrigin.SET_DEFAULT_VALUE
         }
     }
diff --git a/core/commonMain/src/Arguments.kt b/core/commonMain/src/Arguments.kt
index 7a02502..f64ed13 100644
--- a/core/commonMain/src/Arguments.kt
+++ b/core/commonMain/src/Arguments.kt
@@ -160,7 +160,8 @@ fun <T : Any, TResult, DefaultRequired: DefaultRequiredType>
         AbstractSingleArgument<T, TResult, DefaultRequired>.multiple(number: Int): MultipleArgument<T, DefaultRequired> {
     require(number >= 2) { "multiple() modifier with value less than 2 is unavailable. It's already set to 1." }
     val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
-        MultipleArgument<T, DefaultRequired>(ArgDescriptor(type, fullName, number, description, listOfNotNull(defaultValue),
+        MultipleArgument<T, DefaultRequired>(ArgDescriptor(type, fullName, number, description,
+                defaultValue?.toMultiple() ?: SimpleDefaultValue(emptyList()),
                 required, deprecatedWarning), owner)
     }
     owner.entity = newArgument
@@ -173,13 +174,24 @@ fun <T : Any, TResult, DefaultRequired: DefaultRequiredType>
 fun <T : Any, TResult, DefaultRequired: DefaultRequiredType> AbstractSingleArgument<T, TResult, DefaultRequired>.vararg():
         MultipleArgument<T, DefaultRequired> {
     val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
-        MultipleArgument<T, DefaultRequired>(ArgDescriptor(type, fullName, null, description, listOfNotNull(defaultValue),
+        MultipleArgument<T, DefaultRequired>(ArgDescriptor(type, fullName, null, description,
+                defaultValue?.toMultiple() ?: SimpleDefaultValue(emptyList()),
                 required, deprecatedWarning), owner)
     }
     owner.entity = newArgument
     return newArgument
 }
 
+internal fun <T: Any> SingleNullableArgument<T>.toArgumentWithDefault(value: DefaultValue<T>):
+        SingleArgument<T, DefaultRequiredType.Default> {
+    val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
+        SingleArgument<T, DefaultRequiredType.Default>(ArgDescriptor(type, fullName, number, description,
+                value, false, deprecatedWarning), owner)
+    }
+    owner.entity = newArgument
+    return newArgument
+}
+
 /**
  * Specifies the default value for the argument, that will be used when no value is provided for the argument
  * in command line string.
@@ -188,14 +200,20 @@ fun <T : Any, TResult, DefaultRequired: DefaultRequiredType> AbstractSingleArgum
  *
  * @param value the default value.
  */
-fun <T: Any> SingleNullableArgument<T>.default(value: T): SingleArgument<T, DefaultRequiredType.Default> {
-    val newArgument = with((delegate as ParsingValue<T, T>).descriptor as ArgDescriptor) {
-        SingleArgument<T, DefaultRequiredType.Default>(ArgDescriptor(type, fullName, number, description, value,
-            false, deprecatedWarning), owner)
-    }
-    owner.entity = newArgument
-    return newArgument
-}
+fun <T: Any> SingleNullableArgument<T>.default(value: T): SingleArgument<T, DefaultRequiredType.Default> =
+        toArgumentWithDefault(SimpleDefaultValue(value))
+
+
+/**
+ * Specifies the default value for the argument, that will be used when no value is provided for the argument
+ * in command line string.
+ *
+ * Argument becomes optional, because value for it is set even if it isn't provided in command line.
+ *
+ * @param value the default value.
+ */
+fun <T: Any> SingleNullableArgument<T>.default(value: DefaultValuePattern<T>):
+        SingleArgument<T, DefaultRequiredType.Default> = toArgumentWithDefault(value)
 
 /**
  * Specifies the default value for the argument with multiple values, that will be used when no values are provided
@@ -209,8 +227,8 @@ fun <T: Any> MultipleArgument<T, DefaultRequiredType.None>.default(value: Collec
         MultipleArgument<T, DefaultRequiredType.Default> {
     require (value.isNotEmpty()) { "Default value for argument can't be empty collection." }
     val newArgument = with((delegate as ParsingValue<T, List<T>>).descriptor as ArgDescriptor) {
-        MultipleArgument<T, DefaultRequiredType.Default>(ArgDescriptor(type, fullName, number, description, value.toList(),
-                required, deprecatedWarning), owner)
+        MultipleArgument<T, DefaultRequiredType.Default>(ArgDescriptor(type, fullName, number, description,
+                SimpleDefaultValue(value.toList()), required, deprecatedWarning), owner)
     }
     owner.entity = newArgument
     return newArgument
@@ -242,7 +260,7 @@ fun <T: Any> SingleArgument<T, DefaultRequiredType.Required>.optional(): SingleN
 fun <T: Any> MultipleArgument<T, DefaultRequiredType.Required>.optional(): MultipleArgument<T, DefaultRequiredType.None> {
     val newArgument = with((delegate as ParsingValue<T, List<T>>).descriptor as ArgDescriptor) {
         MultipleArgument<T, DefaultRequiredType.None>(ArgDescriptor(type, fullName, number, description,
-                defaultValue?.toList() ?: listOf(), false, deprecatedWarning), owner)
+                defaultValue ?: SimpleDefaultValue(listOf()), false, deprecatedWarning), owner)
     }
     owner.entity = newArgument
     return newArgument
diff --git a/core/commonMain/src/Descriptors.kt b/core/commonMain/src/Descriptors.kt
index 098fc4a..545d333 100644
--- a/core/commonMain/src/Descriptors.kt
+++ b/core/commonMain/src/Descriptors.kt
@@ -4,6 +4,74 @@
  */
 package kotlinx.cli
 
+/**
+ * Wrapper for default value.
+ */
+abstract class DefaultValue<T> {
+    abstract val value: T
+    abstract val helpMessage: String
+
+    /**
+     * Provide text description of value.
+     *
+     * @param value value got getting text description for.
+     */
+    fun valueDescription(value: T) =
+        if (value is List<*> && value.isNotEmpty())
+            " [${value.joinToString()}]"
+        else if (value !is List<*>)
+            " [$value]"
+        else ""
+
+    abstract fun toMultiple(): DefaultValue<List<T>>
+}
+
+/**
+ * Simple default value which just wrap value of any argument type.
+ */
+internal class SimpleDefaultValue<T>(private val simpleValue: T) : DefaultValue<T>() {
+    override val value: T
+        get() = simpleValue
+    override val helpMessage: String
+        get() = valueDescription(value)
+
+    override fun toMultiple(): DefaultValue<List<T>> = SimpleDefaultValue(listOf(value))
+}
+
+/**
+ * Default value pattern which allows to use create default value
+ * based on values of other command line options/arguments.
+ */
+class DefaultValuePattern<T>(val cliEntities: List<CLIEntity<T>>,
+                             val expression: (values: List<T>) -> T,
+                             val helpMessageGenerator: (values: List<String>) -> String) :
+        DefaultValue<T>() {
+
+    init {
+        cliEntities.forEach {
+            with((it.delegate as ParsingValue<*, *>).descriptor) {
+                require(defaultValue != null || required) {
+                    "It's possible to use only arguments/options which always have values."
+                }
+            }
+        }
+    }
+
+    override val value: T by lazy {
+        expression(cliEntities.map { it.value })
+    }
+
+    override val helpMessage: String
+        get() = " [${helpMessageGenerator(cliEntities.
+            map { "\${${(it.delegate as ParsingValue<*, *>).descriptor.fullName!!}}" })}]"
+
+    override fun toMultiple(): DefaultValuePattern<List<T>> {
+        // For custom generator it's impossible to convert value to another type.
+        error("Conversion to multiple default values is unknown in case " +
+                "of provided by user pattern for default value.")
+    }
+}
+
 /**
  * Common descriptor both for options and positional arguments.
  *
@@ -17,7 +85,7 @@ package kotlinx.cli
 internal abstract class Descriptor<T : Any, TResult>(val type: ArgType<T>,
                                                      var fullName: String? = null,
                                                      val description: String? = null,
-                                                     val defaultValue: TResult? = null,
+                                                     val defaultValue: DefaultValue<TResult>? = null,
                                                      val required: Boolean = false,
                                                      val deprecatedWarning: String? = null) {
     /**
@@ -29,19 +97,6 @@ internal abstract class Descriptor<T : Any, TResult>(val type: ArgType<T>,
      */
     abstract val helpMessage: String
 
-    /**
-     * Provide text description of value.
-     *
-     * @param value value got getting text description for.
-     */
-    fun valueDescription(value: TResult?) = value?.let {
-        if (it is List<*> && it.isNotEmpty())
-            " [${it.joinToString()}]"
-        else if (it !is List<*>)
-            " [$it]"
-        else null
-    }
-
     /**
      * Flag to check if descriptor has set default value for option/argument.
      */
@@ -74,7 +129,7 @@ internal class OptionDescriptor<T : Any, TResult>(
         fullName: String? = null,
         val shortName: String ? = null,
         description: String? = null,
-        defaultValue: TResult? = null,
+        defaultValue: DefaultValue<TResult>? = null,
         required: Boolean = false,
         val multiple: Boolean = false,
         val delimiter: String? = null,
@@ -89,7 +144,7 @@ internal class OptionDescriptor<T : Any, TResult>(
             val result = StringBuilder()
             result.append("    $optionFullFormPrefix$fullName")
             shortName?.let { result.append(", $optionShortFromPrefix$it") }
-            valueDescription(defaultValue)?.let {
+            defaultValue?.helpMessage?.let {
                 result.append(it)
             }
             description?.let {result.append(" -> $it")}
@@ -119,7 +174,7 @@ internal class ArgDescriptor<T : Any, TResult>(
         fullName: String?,
         val number: Int? = null,
         description: String? = null,
-        defaultValue: TResult? = null,
+        defaultValue: DefaultValue<TResult>? = null,
         required: Boolean = true,
         deprecatedWarning: String? = null) : Descriptor<T, TResult>(type, fullName, description, defaultValue,
         required, deprecatedWarning) {
@@ -139,7 +194,7 @@ internal class ArgDescriptor<T : Any, TResult>(
         get() {
             val result = StringBuilder()
             result.append("    ${fullName}")
-            valueDescription(defaultValue)?.let {
+            defaultValue?.helpMessage?.let {
                 result.append(it)
             }
             description?.let { result.append(" -> $it") }
diff --git a/core/commonMain/src/Options.kt b/core/commonMain/src/Options.kt
index 2a5508a..c17e6e9 100644
--- a/core/commonMain/src/Options.kt
+++ b/core/commonMain/src/Options.kt
@@ -107,7 +107,7 @@ fun <T : Any, TResult, DefaultType: DefaultRequiredType> AbstractSingleOption<T,
         MultipleOption<T, MultipleOptionType.Repeated, DefaultType>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, listOfNotNull(defaultValue),
+                description, defaultValue?.toMultiple() ?: SimpleDefaultValue(emptyList()),
                 required, true, delimiter, deprecatedWarning
             ), owner
         )
@@ -129,7 +129,7 @@ fun <T : Any, DefaultType: DefaultRequiredType> MultipleOption<T, MultipleOption
         MultipleOption<T, MultipleOptionType.RepeatedDelimited, DefaultRequiredType>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, defaultValue?.toList() ?: listOf(),
+                description, defaultValue ?: SimpleDefaultValue(listOf()),
                 required, true, delimiter, deprecatedWarning
             ), owner
         )
@@ -138,25 +138,37 @@ fun <T : Any, DefaultType: DefaultRequiredType> MultipleOption<T, MultipleOption
     return newOption
 }
 
-/**
- * Specifies the default value for the option, that will be used when no value is provided for it
- * in command line string.
- *
- * @param value the default value.
- */
-fun <T : Any> SingleNullableOption<T>.default(value: T): SingleOption<T, DefaultRequiredType.Default> {
+internal fun <T : Any> SingleNullableOption<T>.toOptionWithDefault(value: DefaultValue<T>): SingleOption<T, DefaultRequiredType.Default> {
     val newOption = with((delegate as ParsingValue<T, T>).descriptor as OptionDescriptor) {
         SingleOption<T, DefaultRequiredType.Default>(
-            OptionDescriptor(
-                optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, value, required, multiple, delimiter, deprecatedWarning
-            ), owner
+                OptionDescriptor(
+                        optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
+                        description, value, required, multiple, delimiter, deprecatedWarning
+                ), owner
         )
     }
     owner.entity = newOption
     return newOption
 }
 
+/**
+ * Specifies the default value for the option, that will be used when no value is provided for it
+ * in command line string.
+ *
+ * @param value the default value.
+ */
+fun <T : Any> SingleNullableOption<T>.default(value: T): SingleOption<T, DefaultRequiredType.Default> =
+        toOptionWithDefault(SimpleDefaultValue(value))
+
+/**
+ * Specifies the default value for the option, that will be used when no value is provided for it
+ * in command line string.
+ *
+ * @param value the default value.
+ */
+fun <T : Any> SingleNullableOption<T>.default(value: DefaultValuePattern<T>):
+        SingleOption<T, DefaultRequiredType.Default> = toOptionWithDefault(value)
+
 /**
  * Specifies the default value for the option with multiple values, that will be used when no values are provided
  * for it in command line string.
@@ -172,7 +184,7 @@ fun <T : Any, OptionType : MultipleOptionType>
         MultipleOption<T, OptionType, DefaultRequiredType.Default>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName,
-                shortName, description, value.toList(),
+                shortName, description, SimpleDefaultValue(value.toList()),
                 required, multiple, delimiter, deprecatedWarning
             ), owner
         )
@@ -208,7 +220,7 @@ fun <T : Any, OptionType : MultipleOptionType>
         MultipleOption<T, OptionType, DefaultRequiredType.Required>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, defaultValue?.toList() ?: listOf(),
+                description, defaultValue ?: SimpleDefaultValue(listOf()),
                 true, multiple, delimiter, deprecatedWarning
             ), owner
         )
@@ -232,7 +244,7 @@ fun <T : Any, DefaultRequired: DefaultRequiredType> AbstractSingleOption<T, *, D
         MultipleOption<T, MultipleOptionType.Delimited, DefaultRequired>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, listOfNotNull(defaultValue),
+                description, defaultValue?.toMultiple() ?: SimpleDefaultValue(emptyList()),
                 required, multiple, delimiterValue, deprecatedWarning
             ), owner
         )
@@ -256,7 +268,7 @@ fun <T : Any, DefaultRequired: DefaultRequiredType> MultipleOption<T, MultipleOp
         MultipleOption<T, MultipleOptionType.RepeatedDelimited, DefaultRequired>(
             OptionDescriptor(
                 optionFullFormPrefix, optionShortFromPrefix, type, fullName, shortName,
-                description, defaultValue?.toList() ?: listOf(),
+                description, defaultValue ?: SimpleDefaultValue(listOf()),
                 required, multiple, delimiterValue, deprecatedWarning
             ), owner
         )
diff --git a/core/commonTest/src/OptionsTests.kt b/core/commonTest/src/OptionsTests.kt
index f1d3156..f5c16e8 100644
--- a/core/commonTest/src/OptionsTests.kt
+++ b/core/commonTest/src/OptionsTests.kt
@@ -64,6 +64,23 @@ class OptionsTests {
         assertEquals("text", renders[0])
     }
 
+    @Test
+    fun testDefaultValuePattern() {
+        val argParser = ArgParser("testParser")
+        val useShortForm by argParser.option(ArgType.Boolean, "short", "s",
+                "Show short version of report").default(false)
+        val renders by argParser.option(ArgType.Choice(listOf("text", "html", "xml", "json")),
+                "renders", "r", "Renders for showing information").multiple().default(listOf("text"))
+        val output = argParser.option(ArgType.String, "output", "o", "Output file")
+                .default("output.txt")
+        val outputLog by argParser.option(ArgType.String, "log", "l", "Output log file")
+                .default(DefaultValuePattern(listOf(output), { values ->  "${values[0]}.log"},
+                        { values -> "${values[0]}.log" } ))
+        argParser.parse(arrayOf("-o", "out.txt"))
+        assertEquals("out.txt.log", outputLog)
+        assertEquals("text", renders[0])
+    }
+
     @Test
     fun testResetOptionsValues() {
         val argParser = ArgParser("testParser")