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diff --git a/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt
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+++ b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt
@@ -0,0 +1,198 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlinx.serialization.Decoder
+import kotlinx.serialization.Encoder
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.Serializer
+import kotlin.math.floor
+import kotlin.math.pow
+import kotlin.math.roundToInt
+
+class AmountParserException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
+class AmountOverflowException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
+
+@Serializable(with = KotlinXAmountSerializer::class)
+data class Amount(
+    /**
+     * name of the currency using either a three-character ISO 4217 currency code,
+     * or a regional currency identifier starting with a "*" followed by at most 10 characters.
+     * ISO 4217 exponents in the name are not supported,
+     * although the "fraction" is corresponds to an ISO 4217 exponent of 6.
+     */
+    val currency: String,
+
+    /**
+     * The integer part may be at most 2^52.
+     * Note that "1" here would correspond to 1 EUR or 1 USD, depending on currency, not 1 cent.
+     */
+    val value: Long,
+
+    /**
+     * Unsigned 32 bit fractional value to be added to value representing
+     * an additional currency fraction, in units of one hundred millionth (1e-8)
+     * of the base currency value.  For example, a fraction
+     * of 50_000_000 would correspond to 50 cents.
+     */
+    val fraction: Int
+) : Comparable<Amount> {
+
+    companion object {
+
+        private const val FRACTIONAL_BASE: Int = 100000000 // 1e8
+
+        private val REGEX_CURRENCY = Regex("""^[-_*A-Za-z0-9]{1,12}$""")
+        val MAX_VALUE = 2.0.pow(52).toLong()
+        private const val MAX_FRACTION_LENGTH = 8
+        const val MAX_FRACTION = 99_999_999
+
+        fun zero(currency: String): Amount {
+            return Amount(checkCurrency(currency), 0, 0)
+        }
+
+        fun fromJSONString(str: String): Amount {
+            val split = str.split(":")
+            if (split.size != 2) throw AmountParserException("Invalid Amount Format")
+            return fromString(split[0], split[1])
+        }
+
+        fun fromString(currency: String, str: String): Amount {
+            // value
+            val valueSplit = str.split(".")
+            val value = checkValue(valueSplit[0].toLongOrNull())
+            // fraction
+            val fraction: Int = if (valueSplit.size > 1) {
+                val fractionStr = valueSplit[1]
+                if (fractionStr.length > MAX_FRACTION_LENGTH)
+                    throw AmountParserException("Fraction $fractionStr too long")
+                val fraction = "0.$fractionStr".toDoubleOrNull()
+                    ?.times(FRACTIONAL_BASE)
+                    ?.roundToInt()
+                checkFraction(fraction)
+            } else 0
+            return Amount(checkCurrency(currency), value, fraction)
+        }
+
+        fun min(currency: String): Amount = Amount(currency, 0, 1)
+        fun max(currency: String): Amount = Amount(currency, MAX_VALUE, MAX_FRACTION)
+
+
+        internal fun checkCurrency(currency: String): String {
+            if (!REGEX_CURRENCY.matches(currency))
+                throw AmountParserException("Invalid currency: $currency")
+            return currency
+        }
+
+        internal fun checkValue(value: Long?): Long {
+            if (value == null || value > MAX_VALUE)
+                throw AmountParserException("Value $value greater than $MAX_VALUE")
+            return value
+        }
+
+        internal fun checkFraction(fraction: Int?): Int {
+            if (fraction == null || fraction > MAX_FRACTION)
+                throw AmountParserException("Fraction $fraction greater than $MAX_FRACTION")
+            return fraction
+        }
+
+    }
+
+    val amountStr: String
+        get() = if (fraction == 0) "$value" else {
+            var f = fraction
+            var fractionStr = ""
+            while (f > 0) {
+                fractionStr += f / (FRACTIONAL_BASE / 10)
+                f = (f * 10) % FRACTIONAL_BASE
+            }
+            "$value.$fractionStr"
+        }
+
+    operator fun plus(other: Amount): Amount {
+        check(currency == other.currency) { "Can only subtract from same currency" }
+        val resultValue = value + other.value + floor((fraction + other.fraction).toDouble() / FRACTIONAL_BASE).toLong()
+        if (resultValue > MAX_VALUE)
+            throw AmountOverflowException()
+        val resultFraction = (fraction + other.fraction) % FRACTIONAL_BASE
+        return Amount(currency, resultValue, resultFraction)
+    }
+
+    operator fun times(factor: Int): Amount {
+        // TODO consider replacing with a faster implementation
+        if (factor == 0) return zero(currency)
+        var result = this
+        for (i in 1 until factor) result += this
+        return result
+    }
+
+    operator fun minus(other: Amount): Amount {
+        check(currency == other.currency) { "Can only subtract from same currency" }
+        var resultValue = value
+        var resultFraction = fraction
+        if (resultFraction < other.fraction) {
+            if (resultValue < 1L)
+                throw AmountOverflowException()
+            resultValue--
+            resultFraction += FRACTIONAL_BASE
+        }
+        check(resultFraction >= other.fraction)
+        resultFraction -= other.fraction
+        if (resultValue < other.value)
+            throw AmountOverflowException()
+        resultValue -= other.value
+        return Amount(currency, resultValue, resultFraction)
+    }
+
+    fun isZero(): Boolean {
+        return value == 0L && fraction == 0
+    }
+
+    fun toJSONString(): String {
+        return "$currency:$amountStr"
+    }
+
+    override fun toString(): String {
+        return "$amountStr $currency"
+    }
+
+    override fun compareTo(other: Amount): Int {
+        check(currency == other.currency) { "Can only compare amounts with the same currency" }
+        when {
+            value == other.value -> {
+                if (fraction < other.fraction) return -1
+                if (fraction > other.fraction) return 1
+                return 0
+            }
+            value < other.value -> return -1
+            else -> return 1
+        }
+    }
+
+}
+
+@Serializer(forClass = Amount::class)
+object KotlinXAmountSerializer: KSerializer<Amount> {
+    override fun serialize(encoder: Encoder, value: Amount) {
+        encoder.encodeString(value.toJSONString())
+    }
+
+    override fun deserialize(decoder: Decoder): Amount {
+        return Amount.fromJSONString(decoder.decodeString())
+    }
+}