diff --git a/class-diagram.png b/class-diagram.png
new file mode 100644
index 000000000..9fd6af458
Binary files /dev/null and b/class-diagram.png differ
diff --git a/src/main/java/com/booleanuk/core/Account.java b/src/main/java/com/booleanuk/core/Account.java
new file mode 100644
index 000000000..7a90a3c36
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/Account.java
@@ -0,0 +1,73 @@
+package com.booleanuk.core;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public abstract class Account {
+    private float balance;
+    private ArrayList<Transaction> transactions = new ArrayList<>();
+
+    Transaction deposit(float amount) {
+        // amount must be greater than 0
+        if (amount <= 0) {
+            return null;
+        }
+
+        balance += amount;
+        Transaction transaction = new Transaction(amount, balance, true);
+        transactions.add(transaction);
+
+        return transaction;
+    }
+
+    Transaction withdraw(float amount) {
+        // amount must be greater than 0 and less than balance
+        if (amount <= 0 || amount > balance) {
+            return null;
+        }
+
+        balance -= amount;
+        Transaction transaction = new Transaction(amount, balance, false);
+        transactions.add(transaction);
+
+        return transaction;
+    }
+
+    float getBalance() {
+        return balance;
+    }
+
+    ArrayList<Transaction> getTransactions() {
+        return transactions;
+    }
+
+    String statement() {
+        StringBuilder sb = new StringBuilder();
+
+        int cellWidth = 30;
+        // format String
+        String format = "| %-" + cellWidth + "s | %-" + cellWidth + "s | %-" + cellWidth + "s | %-" + cellWidth
+                + "s |%n";
+        // add headers
+        sb.append(String.format(format, "Date", "Credit", "Debit", "Balance"));
+
+        List<Transaction> descending = transactions.reversed();
+
+        for (Transaction t : descending) {
+            String time = t.getTime().toString();
+            String amount = String.format("%.2f", t.getAmount());
+            String balanceAfter = String.format("%.2f", t.getBalanceAfter());
+
+            // if deposit
+            if (t.getIsDeposit()) {
+                sb.append(String.format(format, time, amount, "", balanceAfter));
+            }
+            // if withdraw
+            else {
+                sb.append(String.format(format, time, "", amount, balanceAfter));
+            }
+        }
+
+        return sb.toString();
+    }
+}
diff --git a/src/main/java/com/booleanuk/core/CurrentAccount.java b/src/main/java/com/booleanuk/core/CurrentAccount.java
new file mode 100644
index 000000000..727a0f600
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/CurrentAccount.java
@@ -0,0 +1,4 @@
+package com.booleanuk.core;
+
+public class CurrentAccount extends Account {
+}
diff --git a/src/main/java/com/booleanuk/core/SavingsAccount.java b/src/main/java/com/booleanuk/core/SavingsAccount.java
new file mode 100644
index 000000000..b9efb328e
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/SavingsAccount.java
@@ -0,0 +1,5 @@
+package com.booleanuk.core;
+
+public class SavingsAccount extends Account {
+
+}
diff --git a/src/main/java/com/booleanuk/core/Transaction.java b/src/main/java/com/booleanuk/core/Transaction.java
new file mode 100644
index 000000000..32dc3dac1
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/Transaction.java
@@ -0,0 +1,33 @@
+package com.booleanuk.core;
+
+import java.time.LocalDateTime;
+
+public class Transaction {
+    private LocalDateTime time;
+    private float amount;
+    private float balanceAfter;
+    private boolean isDeposit;
+
+    public Transaction(float amount, float balanceAfter, boolean isDeposit) {
+        this.time = LocalDateTime.now();
+        this.amount = amount;
+        this.balanceAfter = balanceAfter;
+        this.isDeposit = isDeposit;
+    }
+
+    LocalDateTime getTime() {
+        return time;
+    }
+
+    float getAmount() {
+        return amount;
+    }
+
+    float getBalanceAfter() {
+        return balanceAfter;
+    }
+
+    boolean getIsDeposit() {
+        return isDeposit;
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/Account.java b/src/main/java/com/booleanuk/extension/Account.java
new file mode 100644
index 000000000..6f49ae27d
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/Account.java
@@ -0,0 +1,87 @@
+package com.booleanuk.extension;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public abstract class Account {
+    private ArrayList<Transaction> transactions = new ArrayList<>();
+    private long accountNr;
+
+    public Account(long accountNr) {
+        this.accountNr = accountNr;
+    }
+
+    Transaction deposit(float amount) {
+        // amount must be greater than 0
+        if (amount <= 0) {
+            return null;
+        }
+
+        Transaction transaction = new Transaction(amount, getBalance() + amount, true);
+        transactions.add(transaction);
+
+        return transaction;
+    }
+
+    Transaction withdraw(float amount) {
+        // amount must be greater than 0 and less than getBalance()
+        if (amount <= 0 || amount > getBalance()) {
+            return null;
+        }
+
+        Transaction transaction = new Transaction(amount, getBalance() - amount, false);
+        transactions.add(transaction);
+
+        return transaction;
+    }
+
+    float getBalance() {
+        float balance = 0f;
+        for (Transaction t : transactions) {
+            if (t.getIsDeposit()) {
+                balance += t.getAmount();
+            } else {
+                balance -= t.getAmount();
+            }
+        }
+        return balance;
+    }
+
+    ArrayList<Transaction> getTransactions() {
+        return transactions;
+    }
+
+    String statement() {
+        StringBuilder sb = new StringBuilder();
+
+        int cellWidth = 30;
+        // format String
+        String format = "| %-" + cellWidth + "s | %-" + cellWidth + "s | %-" + cellWidth + "s | %-" + cellWidth
+                + "s |%n";
+        // add headers
+        sb.append(String.format(format, "Date", "Credit", "Debit", "Balance"));
+
+        List<Transaction> descending = transactions.reversed();
+
+        for (Transaction t : descending) {
+            String time = t.getTime().toString();
+            String amount = String.format("%.2f", t.getAmount());
+            String balanceAfter = String.format("%.2f", t.getBalanceAfter());
+
+            // if deposit
+            if (t.getIsDeposit()) {
+                sb.append(String.format(format, time, amount, "", balanceAfter));
+            }
+            // if withdraw
+            else {
+                sb.append(String.format(format, time, "", amount, balanceAfter));
+            }
+        }
+
+        return sb.toString();
+    }
+
+    long getAccountNr() {
+        return accountNr;
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/Bank.java b/src/main/java/com/booleanuk/extension/Bank.java
new file mode 100644
index 000000000..630635bb4
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/Bank.java
@@ -0,0 +1,20 @@
+package com.booleanuk.extension;
+
+import java.util.HashMap;
+
+public class Bank {
+    private HashMap<Integer, Branch> branches = new HashMap<>();
+    private int nextBranchId = 1000;
+
+    Branch newBranch() {
+        Branch branch = new Branch(nextBranchId);
+        branches.put(nextBranchId, branch);
+        nextBranchId++;
+
+        return branch;
+    }
+
+    HashMap<Integer, Branch> getBranches() {
+        return branches;
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/Branch.java b/src/main/java/com/booleanuk/extension/Branch.java
new file mode 100644
index 000000000..7c90d9161
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/Branch.java
@@ -0,0 +1,37 @@
+package com.booleanuk.extension;
+
+import java.util.HashMap;
+
+public class Branch {
+    private int nextAccountId = 10000000;
+    private HashMap<Long, Account> accounts = new HashMap<>();
+    private int branchId;
+
+    public Branch(int branchId) {
+        this.branchId = branchId;
+    }
+
+    int getId() {
+        return branchId;
+    }
+
+    HashMap<Long, Account> getAccounts() {
+        return accounts;
+    }
+
+    CurrentAccount newCurrentAccount() {
+        long accountNr = Long.parseLong(String.valueOf(branchId) + String.valueOf(nextAccountId));
+        nextAccountId++;
+        CurrentAccount acc = new CurrentAccount(accountNr);
+        accounts.put(accountNr, acc);
+        return acc;
+    }
+
+    SavingsAccount newSavingsAccount() {
+        long accountNr = Long.parseLong(String.valueOf(branchId) + String.valueOf(nextAccountId));
+        nextAccountId++;
+        SavingsAccount acc = new SavingsAccount(accountNr);
+        accounts.put(accountNr, acc);
+        return acc;
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/CurrentAccount.java b/src/main/java/com/booleanuk/extension/CurrentAccount.java
new file mode 100644
index 000000000..c6fc00ebb
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/CurrentAccount.java
@@ -0,0 +1,7 @@
+package com.booleanuk.extension;
+
+public class CurrentAccount extends Account {
+    public CurrentAccount(long accountNr) {
+        super(accountNr);
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/SavingsAccount.java b/src/main/java/com/booleanuk/extension/SavingsAccount.java
new file mode 100644
index 000000000..8927edae9
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/SavingsAccount.java
@@ -0,0 +1,7 @@
+package com.booleanuk.extension;
+
+public class SavingsAccount extends Account {
+    public SavingsAccount(long accountNr) {
+        super(accountNr);
+    }
+}
diff --git a/src/main/java/com/booleanuk/extension/Transaction.java b/src/main/java/com/booleanuk/extension/Transaction.java
new file mode 100644
index 000000000..9489ae306
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/Transaction.java
@@ -0,0 +1,33 @@
+package com.booleanuk.extension;
+
+import java.time.LocalDateTime;
+
+public class Transaction {
+    private LocalDateTime time;
+    private float amount;
+    private float balanceAfter;
+    private boolean isDeposit;
+
+    public Transaction(float amount, float balanceAfter, boolean isDeposit) {
+        this.time = LocalDateTime.now();
+        this.amount = amount;
+        this.balanceAfter = balanceAfter;
+        this.isDeposit = isDeposit;
+    }
+
+    LocalDateTime getTime() {
+        return time;
+    }
+
+    float getAmount() {
+        return amount;
+    }
+
+    float getBalanceAfter() {
+        return balanceAfter;
+    }
+
+    boolean getIsDeposit() {
+        return isDeposit;
+    }
+}
diff --git a/src/test/java/com/booleanuk/core/TestAccount.java b/src/test/java/com/booleanuk/core/TestAccount.java
new file mode 100644
index 000000000..349fa1d48
--- /dev/null
+++ b/src/test/java/com/booleanuk/core/TestAccount.java
@@ -0,0 +1,98 @@
+package com.booleanuk.core;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+public class TestAccount {
+    @Test
+    void testDeposit() {
+        Account acc = new CurrentAccount();
+
+        Assertions.assertEquals(0f, acc.getBalance());
+        Transaction tran = acc.deposit(2500.50f);
+        Assertions.assertEquals(2500.50f, acc.getBalance());
+
+        // check if transaction was created correctly
+        Assertions.assertTrue(tran.getTime() != null);
+        Assertions.assertEquals(2500.50f, tran.getAmount());
+        Assertions.assertEquals(2500.50f, tran.getBalanceAfter());
+        Assertions.assertTrue(tran.getIsDeposit());
+    }
+
+    @Test
+    void testInvalidDeposit() {
+        Account acc = new CurrentAccount();
+
+        Transaction tran = acc.deposit(-1000f);
+        Assertions.assertEquals(0f, acc.getBalance());
+
+        Assertions.assertTrue(tran == null);
+    }
+
+    @Test
+    void testValidWithdraw() {
+        Account acc = new CurrentAccount();
+
+        Assertions.assertEquals(0f, acc.getBalance());
+        acc.deposit(2500f);
+        Transaction tran = acc.withdraw(1000f);
+        Assertions.assertEquals(1500f, acc.getBalance());
+
+        // check if transaction was created correctly
+        Assertions.assertTrue(tran.getTime() != null);
+        Assertions.assertEquals(1000f, tran.getAmount());
+        Assertions.assertEquals(1500f, tran.getBalanceAfter());
+        Assertions.assertFalse(tran.getIsDeposit());
+    }
+
+    @Test
+    void testInvalidWithdraw() {
+        Account acc = new CurrentAccount();
+
+        acc.deposit(1000f);
+        Transaction tran = acc.withdraw(-1000f);
+        Assertions.assertTrue(tran == null);
+
+        tran = acc.withdraw(1000.1f);
+        Assertions.assertTrue(tran == null);
+
+        Assertions.assertEquals(1000f, acc.getBalance());
+    }
+
+    @Test
+    void testAccountStatement() {
+        Account acc = new CurrentAccount();
+
+        acc.deposit(1000f);
+        acc.deposit(2000f);
+        acc.withdraw(500f);
+
+        String[] statement = acc.statement().split("\n");
+
+        String expected = "|Date|Credit|Debit|Balance|\n"
+                + "|14/01/2012||500.00|2500.00|\n"
+                + "|14/01/2012|2000.00||3000.00|\n"
+                + "|14/01/2012|1000.00||1000.00|\n";
+        String[] expectedLines = expected.split("\n");
+
+        Assertions.assertEquals(expectedLines.length, statement.length);
+
+        for (int i = 0; i < statement.length; i++) {
+            String line = statement[i];
+
+            String[] cells = line.strip().split("\\|");
+            String[] expectedCells = expectedLines[i].strip().split("\\|");
+
+            Assertions.assertEquals(expectedCells.length, cells.length);
+
+            // skip date cell
+            for (int n = 0; n < cells.length; n++) {
+                // if transaction line, skip date
+                if (i > 0 && n <= 1) {
+                    continue;
+                }
+                Assertions.assertEquals(expectedCells[n].strip(), cells[n].strip());
+            }
+        }
+    }
+}
diff --git a/src/test/java/com/booleanuk/extension/TestAccount.java b/src/test/java/com/booleanuk/extension/TestAccount.java
new file mode 100644
index 000000000..2d1ed4508
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TestAccount.java
@@ -0,0 +1,98 @@
+package com.booleanuk.extension;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+public class TestAccount {
+    @Test
+    void testDeposit() {
+        Account acc = new CurrentAccount(1);
+
+        Assertions.assertEquals(0f, acc.getBalance());
+        Transaction tran = acc.deposit(2500.50f);
+        Assertions.assertEquals(2500.50f, acc.getBalance());
+
+        // check if transaction was created correctly
+        Assertions.assertTrue(tran.getTime() != null);
+        Assertions.assertEquals(2500.50f, tran.getAmount());
+        Assertions.assertEquals(2500.50f, tran.getBalanceAfter());
+        Assertions.assertTrue(tran.getIsDeposit());
+    }
+
+    @Test
+    void testInvalidDeposit() {
+        Account acc = new CurrentAccount(1);
+
+        Transaction tran = acc.deposit(-1000f);
+        Assertions.assertEquals(0f, acc.getBalance());
+
+        Assertions.assertTrue(tran == null);
+    }
+
+    @Test
+    void testValidWithdraw() {
+        Account acc = new CurrentAccount(1);
+
+        Assertions.assertEquals(0f, acc.getBalance());
+        acc.deposit(2500f);
+        Transaction tran = acc.withdraw(1000f);
+        Assertions.assertEquals(1500f, acc.getBalance());
+
+        // check if transaction was created correctly
+        Assertions.assertTrue(tran.getTime() != null);
+        Assertions.assertEquals(1000f, tran.getAmount());
+        Assertions.assertEquals(1500f, tran.getBalanceAfter());
+        Assertions.assertFalse(tran.getIsDeposit());
+    }
+
+    @Test
+    void testInvalidWithdraw() {
+        Account acc = new CurrentAccount(1);
+
+        acc.deposit(1000f);
+        Transaction tran = acc.withdraw(-1000f);
+        Assertions.assertTrue(tran == null);
+
+        tran = acc.withdraw(1000.1f);
+        Assertions.assertTrue(tran == null);
+
+        Assertions.assertEquals(1000f, acc.getBalance());
+    }
+
+    @Test
+    void testAccountStatement() {
+        Account acc = new CurrentAccount(1);
+
+        acc.deposit(1000f);
+        acc.deposit(2000f);
+        acc.withdraw(500f);
+
+        String[] statement = acc.statement().split("\n");
+
+        String expected = "|Date|Credit|Debit|Balance|\n"
+                + "|14/01/2012||500.00|2500.00|\n"
+                + "|14/01/2012|2000.00||3000.00|\n"
+                + "|14/01/2012|1000.00||1000.00|\n";
+        String[] expectedLines = expected.split("\n");
+
+        Assertions.assertEquals(expectedLines.length, statement.length);
+
+        for (int i = 0; i < statement.length; i++) {
+            String line = statement[i];
+
+            String[] cells = line.strip().split("\\|");
+            String[] expectedCells = expectedLines[i].strip().split("\\|");
+
+            Assertions.assertEquals(expectedCells.length, cells.length);
+
+            // skip date cell
+            for (int n = 0; n < cells.length; n++) {
+                // if transaction line, skip date
+                if (i > 0 && n <= 1) {
+                    continue;
+                }
+                Assertions.assertEquals(expectedCells[n].strip(), cells[n].strip());
+            }
+        }
+    }
+}
diff --git a/src/test/java/com/booleanuk/extension/TestBank.java b/src/test/java/com/booleanuk/extension/TestBank.java
new file mode 100644
index 000000000..51305e14d
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TestBank.java
@@ -0,0 +1,19 @@
+package com.booleanuk.extension;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+public class TestBank {
+    @Test
+    void testNewBranch() {
+        Bank bank = new Bank();
+
+        Branch branch = bank.newBranch();
+        Assertions.assertEquals(1000, branch.getId());
+        Assertions.assertEquals(1, bank.getBranches().size()); // check if added to map
+
+        branch = bank.newBranch();
+        Assertions.assertEquals(1001, branch.getId());
+        Assertions.assertEquals(2, bank.getBranches().size()); // check if added to map
+    }
+}
diff --git a/src/test/java/com/booleanuk/extension/TestBranch.java b/src/test/java/com/booleanuk/extension/TestBranch.java
new file mode 100644
index 000000000..161c96f6e
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TestBranch.java
@@ -0,0 +1,28 @@
+package com.booleanuk.extension;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+public class TestBranch {
+    @Test
+    void testNewCurrentAccount() {
+        Bank bank = new Bank();
+        Branch branch = bank.newBranch();
+
+        CurrentAccount acc = branch.newCurrentAccount();
+
+        Assertions.assertEquals(1, branch.getAccounts().size());
+        Assertions.assertEquals(100010000000L, acc.getAccountNr());
+    }
+
+    @Test
+    void testNewSavingsAccount() {
+        Bank bank = new Bank();
+        Branch branch = bank.newBranch();
+
+        SavingsAccount acc = branch.newSavingsAccount();
+
+        Assertions.assertEquals(1, branch.getAccounts().size());
+        Assertions.assertEquals(100010000000L, acc.getAccountNr());
+    }
+}