diff --git a/src/main/java/eu/ztsh/wymiana/exception/InsufficientFundsException.java b/src/main/java/eu/ztsh/wymiana/exception/InsufficientFundsException.java
new file mode 100644
index 0000000..4c8f314
--- /dev/null
+++ b/src/main/java/eu/ztsh/wymiana/exception/InsufficientFundsException.java
@@ -0,0 +1,9 @@
+package eu.ztsh.wymiana.exception;
+
+public class InsufficientFundsException extends RuntimeException {
+
+    public InsufficientFundsException() {
+        super("Insufficient funds");
+    }
+
+}
diff --git a/src/main/java/eu/ztsh/wymiana/service/CurrencyService.java b/src/main/java/eu/ztsh/wymiana/service/CurrencyService.java
new file mode 100644
index 0000000..53d401e
--- /dev/null
+++ b/src/main/java/eu/ztsh/wymiana/service/CurrencyService.java
@@ -0,0 +1,21 @@
+package eu.ztsh.wymiana.service;
+
+import eu.ztsh.wymiana.model.User;
+import eu.ztsh.wymiana.validation.InstanceValidator;
+import eu.ztsh.wymiana.web.model.CurrencyExchangeRequest;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+@RequiredArgsConstructor
+@Service
+public class CurrencyService {
+
+    private final UserService userService;
+    private final NbpService nbpService;
+    private final InstanceValidator validator;
+
+    public User exchange(CurrencyExchangeRequest request) {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+}
diff --git a/src/test/java/eu/ztsh/wymiana/service/CurrencyServiceTest.java b/src/test/java/eu/ztsh/wymiana/service/CurrencyServiceTest.java
new file mode 100644
index 0000000..c49396c
--- /dev/null
+++ b/src/test/java/eu/ztsh/wymiana/service/CurrencyServiceTest.java
@@ -0,0 +1,50 @@
+package eu.ztsh.wymiana.service;
+
+import eu.ztsh.wymiana.EntityCreator;
+import eu.ztsh.wymiana.RepositoryBasedTest;
+import eu.ztsh.wymiana.data.repository.UserRepository;
+import eu.ztsh.wymiana.exception.InsufficientFundsException;
+import eu.ztsh.wymiana.validation.InstanceValidator;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import static eu.ztsh.wymiana.EntityCreator.Constants.*;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class CurrencyServiceTest extends RepositoryBasedTest {
+
+    private final CurrencyService currencyService;
+
+    @Autowired
+    public CurrencyServiceTest(UserRepository userRepository, InstanceValidator instanceValidator) {
+        super(userRepository);
+        var nbp = Mockito.mock(NbpService.class);
+        Mockito.when(nbp.getSellRate("USD")).thenReturn(USD_SELL);
+        Mockito.when(nbp.getBuyRate("USD")).thenReturn(USD_BUY);
+        currencyService = new CurrencyService(new UserService(userRepository, instanceValidator), nbp, instanceValidator);
+    }
+
+    @Test
+    void successTest() {
+        var result = currencyService.exchange(EntityCreator.exchangeRequest()
+            .from(PLN_SYMBOL)
+            .to(USD_SYMBOL)
+            .toSell(PLN)
+            .build());
+        assertThat(result.currencies())
+            .matches(map -> map.get(PLN_SYMBOL).amount() == 0 && map.get(USD_SYMBOL).amount() == USD_BUY);
+    }
+
+    @Test
+    void insufficientFundsTest() {
+        assertThatThrownBy(() -> currencyService.exchange(EntityCreator.exchangeRequest()
+            .from(PLN_SYMBOL)
+            .to(USD_SYMBOL)
+            .toBuy(PLN)
+            .build()))
+            .isInstanceOf(InsufficientFundsException.class);
+    }
+
+}