diff --git a/invoice.php b/invoice.php
index 6e752bf0..6e87a880 100644
--- a/invoice.php
+++ b/invoice.php
@@ -3,9 +3,6 @@
 <?php 
 
 if(isset($_GET['invoice_id'])){
-  $invoice_subtotal = 0.00;
-  $invoice_tax = 0.00;
-  $invoice_total = 0.00;
 
   $invoice_id = intval($_GET['invoice_id']);
 
@@ -20,12 +17,7 @@ if(isset($_GET['invoice_id'])){
   $invoice_status = $row['invoice_status'];
   $invoice_date = $row['invoice_date'];
   $invoice_due = $row['invoice_due'];
-  $invoice_subtotal = $row['invoice_subtotal'];
-  $invoice_discount = $row['invoice_discount'];
-  $invoice_tax = $row['invoice_tax'];
-  $invoice_total = $row['invoice_total'];
-  $invoice_paid = $row['invoice_paid'];
-  $invoice_balance = $row['invoice_balance'];
+  $invoice_amount = $row['invoice_amount'];
   $client_id = $row['client_id'];
   $client_name = $row['client_name'];
   $client_address = $row['client_address'];
@@ -39,8 +31,16 @@ if(isset($_GET['invoice_id'])){
   }
   $client_website = $row['client_website'];
 
-  $sql2 = mysqli_query($mysqli,"SELECT * FROM invoice_history WHERE invoice_id = $invoice_id ORDER BY invoice_history_id DESC");
-  $sql3 = mysqli_query($mysqli,"SELECT * FROM invoice_payments, accounts WHERE invoice_payments.account_id = accounts.account_id AND invoice_payments.invoice_id = $invoice_id ORDER BY invoice_payments.invoice_payment_id DESC");
+  $sql_invoice_history = mysqli_query($mysqli,"SELECT * FROM invoice_history WHERE invoice_id = $invoice_id ORDER BY invoice_history_id DESC");
+  
+  $sql_payments = mysqli_query($mysqli,"SELECT * FROM invoice_payments, accounts WHERE invoice_payments.account_id = accounts.account_id AND invoice_payments.invoice_id = $invoice_id ORDER BY invoice_payments.invoice_payment_id DESC");
+
+  //Add up all the payments for the invoice and get the total amount paid to the invoice
+  $sql_amount_paid = mysqli_query($mysqli,"SELECT SUM(invoice_payment_amount) AS amount_paid FROM invoice_payments WHERE invoice_id = $invoice_id");
+  $row = mysqli_fetch_array($sql_amount_paid);
+  $amount_paid = $row['amount_paid'];
+
+  $balance = $invoice_amount - $amount_paid;
 
   //check to see if overdue
 
@@ -82,7 +82,7 @@ if(isset($_GET['invoice_id'])){
         <a class="dropdown-item" href="#" data-toggle="modal" data-target="#editinvoiceModal<?php echo $invoice_id; ?>">Edit</a>
         <a class="dropdown-item" href="#" data-toggle="modal" data-target="#addinvoiceCopyModal<?php echo $invoice_id; ?>">Copy</a>
         <a class="dropdown-item" href="email_invoice.php?invoice_id=<?php echo $invoice_id; ?>">Send Email</a>
-        <a class="dropdown-item" href="#" data-toggle="modal" data-target="#addInvoicePaymentModal">Add Payment</a>
+        <?php if($invoice_status !== "Paid"){ ?><a class="dropdown-item" href="#" data-toggle="modal" data-target="#addInvoicePaymentModal">Add Payment</a><?php } ?>
         <a class="dropdown-item" href="#" data-toggle="modal" data-target="#addinvoiceCopyModal<?php echo $invoice_id; ?>">Print</a>
         <a class="dropdown-item" href="#">Delete</a>
       </div>
@@ -219,8 +219,20 @@ if(isset($_GET['invoice_id'])){
             <tr>
               <td colspan="5"></td>
               <td><strong>Total</strong></td>
-              <td class="text-right">$<?php echo number_format($invoice_total,2); ?></td>
+              <td class="text-right">$<?php echo number_format($invoice_amount,2); ?></td>
             </tr>
+            <?php if($amount_paid > 0){ ?>
+            <tr>
+              <td colspan="5"></td>
+              <td><strong>Paid</strong></td>
+              <td class="text-right text-success">$<?php echo number_format($amount_paid,2); ?></td>
+            </tr>
+            <tr>
+              <td colspan="5"></td>
+              <td><strong>Balance</strong></td>
+              <td class="text-right">$<?php echo number_format($balance,2); ?></td>
+            </tr>
+          <?php } ?>
           </tbody>
         </table>   
     </div>
@@ -278,7 +290,7 @@ if(isset($_GET['invoice_id'])){
           <tbody>
             <?php
       
-            while($row = mysqli_fetch_array($sql2)){
+            while($row = mysqli_fetch_array($sql_invoice_history)){
               $invoice_history_date = $row['invoice_history_date'];
               $invoice_history_status = $row['invoice_history_status'];
               $invoice_history_description = $row['invoice_history_description'];
@@ -316,7 +328,7 @@ if(isset($_GET['invoice_id'])){
           <tbody>
             <?php
       
-            while($row = mysqli_fetch_array($sql3)){
+            while($row = mysqli_fetch_array($sql_payments)){
               $invoice_payment_id = $row['invoice_payment_id'];
               $invoice_payment_date = $row['invoice_payment_date'];
               $invoice_payment_amount = $row['invoice_payment_amount'];
diff --git a/invoices.php b/invoices.php
index 7b869707..a6746abb 100644
--- a/invoices.php
+++ b/invoices.php
@@ -35,7 +35,7 @@
             $invoice_status = $row['invoice_status'];
             $invoice_date = $row['invoice_date'];
             $invoice_due = $row['invoice_due'];
-            $invoice_balance = $row['invoice_balance'];
+            $invoice_amount = $row['invoice_amount'];
             $client_id = $row['client_id'];
             $client_name = $row['client_name'];
 
@@ -64,7 +64,7 @@
           <tr>
             <td><a href="invoice.php?invoice_id=<?php echo $invoice_id; ?>">INV-<?php echo "$invoice_number"; ?></a></td>
             <td><a href="client.php?client_id=<?php echo $client_id; ?>"><?php echo "$client_name"; ?></a></td>
-            <td class="text-right text-monospace">$<?php echo number_format($invoice_balance,2); ?></td>
+            <td class="text-right text-monospace">$<?php echo number_format($invoice_amount,2); ?></td>
             <td><?php echo "$invoice_date"; ?></td>
             <td><div class="<?php echo $overdue_color; ?>"><?php echo "$invoice_due"; ?></div></td>
             <td>
diff --git a/post.php b/post.php
index 20214b32..87ffab1a 100644
--- a/post.php
+++ b/post.php
@@ -423,12 +423,9 @@ if(isset($_POST['add_invoice_item'])){
     $sql = mysqli_query($mysqli,"SELECT * FROM invoices WHERE invoice_id = $invoice_id");
     $row = mysqli_fetch_array($sql);
 
-    $invoice_subtotal = $row['invoice_subtotal'] + $subtotal;
-    $invoice_tax = $row['invoice_tax'] + $tax; 
-    $invoice_total = $row['invoice_total'] + $total;
-    $invoice_balance = $row['invoice_balance'] + $total;
+    $new_invoice_amount = $row['invoice_amount'] + $total;
 
-    mysqli_query($mysqli,"UPDATE invoices SET invoice_subtotal = '$invoice_subtotal', invoice_tax = '$invoice_tax', invoice_total = '$invoice_total', invoice_balance = '$invoice_balance' WHERE invoice_id = $invoice_id");
+    mysqli_query($mysqli,"UPDATE invoices SET invoice_amount = '$new_invoice_amount' WHERE invoice_id = $invoice_id");
 
     $_SESSION['alert_message'] = "Item added";
     
@@ -448,12 +445,10 @@ if(isset($_GET['delete_invoice_item'])){
 
     $sql = mysqli_query($mysqli,"SELECT * FROM invoices WHERE invoice_id = $invoice_id");
     $row = mysqli_fetch_array($sql);
-    $invoice_balance = $row['invoice_balance'] - $invoice_item_total;
-    $invoice_subtotal = $row['invoice_subtotal'] - $invoice_item_subtotal;
-    $invoice_tax = $row['invoice_tax'] - $invoice_item_tax;
-    $invoice_total = $row['invoice_total'] - $invoice_item_total;
+    
+    $new_invoice_amount = $row['invoice_amount'] - $invoice_item_total;
 
-    mysqli_query($mysqli,"UPDATE invoices SET invoice_subtotal = '$invoice_subtotal', invoice_tax = '$invoice_tax', invoice_total = '$invoice_total', invoice_balance = '$invoice_balance' WHERE invoice_id = $invoice_id");
+    mysqli_query($mysqli,"UPDATE invoices SET invoice_amount = '$new_invoice_amount' WHERE invoice_id = $invoice_id");
 
     mysqli_query($mysqli,"DELETE FROM invoice_items WHERE invoice_item_id = $invoice_item_id");
 
@@ -471,14 +466,30 @@ if(isset($_POST['add_invoice_payment'])){
     $account = intval($_POST['account']);
     $payment_method = strip_tags(mysqli_real_escape_string($mysqli,$_POST['payment_method']));
 
+    mysqli_query($mysqli,"INSERT INTO invoice_payments SET invoice_payment_date = '$date', invoice_payment_amount = '$amount', account_id = $account, invoice_payment_method = '$payment_method', invoice_id = $invoice_id");
+
+    //Add up all the payments for the invoice and get the total amount paid to the invoice
+    $sql_total_payments_amount = mysqli_query($mysqli,"SELECT SUM(invoice_payment_amount) AS total_payments_amount FROM invoice_payments WHERE invoice_id = $invoice_id");
+    $row = mysqli_fetch_array($sql_total_payments_amount);
+    $total_payments_amount = $row['total_payments_amount'];
+    
+    //Get the invoice total
     $sql = mysqli_query($mysqli,"SELECT * FROM invoices WHERE invoice_id = $invoice_id");
     $row = mysqli_fetch_array($sql);
-    $invoice_balance = $row['invoice_balance'] - $amount;
-    $invoice_paid = $row['invoice_paid'] + $paid;
+    $invoice_amount = $row['invoice_amount'];
 
-    mysqli_query($mysqli,"UPDATE invoices SET invoice_balance = '$invoice_balance', invoice_paid = '$invoice_paid' WHERE invoice_id = $invoice_id");
+    //Calculate the Invoice balance
+    $invoice_balance = $invoice_amount - $total_payments_amount;
 
-    mysqli_query($mysqli,"INSERT INTO invoice_payments SET invoice_payment_date = '$date', invoice_payment_amount = '$amount', account_id = $account, invoice_payment_method = '$payment_method', invoice_id = $invoice_id");
+    //Determine if invoice has been paid
+    if($invoice_balance == 0){
+        $invoice_status = "Paid";
+    }else{
+        $invoice_status = "Partial";
+    }
+
+    //Update Invoice Status
+    mysqli_query($mysqli,"UPDATE invoices SET invoice_status = '$invoice_status' WHERE invoice_id = $invoice_id");
 
     $_SESSION['alert_message'] = "Payment added";
     
@@ -489,14 +500,33 @@ if(isset($_POST['add_invoice_payment'])){
 if(isset($_GET['delete_invoice_payment'])){
     $invoice_payment_id = intval($_GET['delete_invoice_payment']);
 
-    $sql = mysqli_query($mysqli,"SELECT * FROM invoice_payments WHERE invoice_payment_id = $invoice_id");
+    $sql = mysqli_query($mysqli,"SELECT * FROM invoice_payments WHERE invoice_payment_id = $invoice_payment_id");
     $row = mysqli_fetch_array($sql);
     $invoice_id = $row['invoice_id'];
-    $invoice_payment_amount = $row['invoice_payment_amount'];
+    $deleted_payment_amount = $row['invoice_payment_amount'];
 
-    $invoice_balance = $row['invoice_balance'] - $invoice_payment_amount;
+    //Add up all the payments for the invoice and get the total amount paid to the invoice
+    $sql_total_payments_amount = mysqli_query($mysqli,"SELECT SUM(invoice_payment_amount) AS total_payments_amount FROM invoice_payments WHERE invoice_id = $invoice_id");
+    $row = mysqli_fetch_array($sql_total_payments_amount);
+    $total_payments_amount = $row['total_payments_amount'];
+    
+    //Get the invoice total
+    $sql = mysqli_query($mysqli,"SELECT * FROM invoices WHERE invoice_id = $invoice_id");
+    $row = mysqli_fetch_array($sql);
+    $invoice_amount = $row['invoice_amount'];
 
-    mysqli_query($mysqli,"UPDATE invoices SET invoice_balance = '$invoice_balance' WHERE invoice_id = $invoice_id");
+    //Calculate the Invoice balance
+    $invoice_balance = $invoice_amount - $total_payments_amount + $deleted_payment_amount;
+
+    //Determine if invoice has been paid
+    if($invoice_balance == 0){
+        $invoice_status = "Paid";
+    }else{
+        $invoice_status = "Partial";
+    }
+
+    //Update Invoice Status
+    mysqli_query($mysqli,"UPDATE invoices SET invoice_status = '$invoice_status' WHERE invoice_id = $invoice_id");
 
     mysqli_query($mysqli,"DELETE FROM invoice_payments WHERE invoice_payment_id = $invoice_payment_id");