diff --git a/calc.html b/calc.html
index b80dbc1..d7a20b8 100644
--- a/calc.html
+++ b/calc.html
@@ -1,12 +1,24 @@
-<!-- SCD Bond Calculator — WordPress Custom HTML Block -->
+<!-- =================================================================== -->
+<!-- SCD Bond Calculator — WordPress Custom HTML Block               -->
+<!-- Self-contained widget for Stirchley Community Development's     -->
+<!-- bond investment calculator.  All styles are inline to remain    -->
+<!-- portable across WordPress theme environments.                   -->
+<!-- =================================================================== -->
 
 <div id="scd-calc" style="max-width:640px;margin:0 auto;padding:28px 24px;font-family:inherit;color:#2d2d2d;line-height:1.7;">
 
+  <!-- Heading -->
   <h3 style="margin-bottom:12px;font-size:22px;">🧮 Estimate Your Bond Return</h3>
 
+  <!-- Mandatory risk disclaimer — required for FCA compliance -->
   <p style="margin-bottom:28px;font-size:16px;line-height:1.7;color:#2d2d2d;"><em>Illustrative only — not financial advice. Bonds are not FSCS-protected. You may lose some or all of your investment.</em></p>
 
-  <!-- Inputs -->
+  <!-- =============================================================== -->
+  <!-- INPUT FIELDS                                                     -->
+  <!-- Three core parameters: amount, interest rate, term.  Each has    -->
+  <!-- realistic min/max constraints enforced by the HTML attributes    -->
+  <!-- as well as by JS validation in run().                           -->
+  <!-- =============================================================== -->
   <div style="display:flex;gap:16px;flex-wrap:wrap;margin-bottom:32px;">
 
     <div style="flex:1;min-width:180px;">
@@ -32,7 +44,14 @@
 
   </div>
 
-  <!-- Interest method -->
+  <!-- =============================================================== -->
+  <!-- INTEREST PAYOUT METHOD SELECTOR                                 -->
+  <!-- Four radio buttons covering the two binary choices:             -->
+  <!--   Compound (cm/ca)  vs  Simple (sm/sa)                         -->
+  <!--   At maturity (cm/sm)  vs  Paid yearly (ca/sa)                 -->
+  <!-- Values are two-letter codes: first letter = type (c/s),        -->
+  <!-- second letter = schedule (m/a).                                -->
+  <!-- =============================================================== -->
   <p style="font-size:16px;font-weight:600;margin-bottom:12px;color:#2d2d2d;">📈 Interest payout</p>
   <div style="display:flex;gap:12px;flex-wrap:wrap;margin-bottom:36px;">
     <label style="cursor:pointer;padding:12px 18px;border:2px solid #9a9a9a;border-radius:8px;font-size:16px;background:#fff;display:flex;align-items:center;gap:8px;color:#2d2d2d;">
@@ -53,16 +72,29 @@
     </label>
   </div>
 
-  <!-- Button -->
+  <!-- =============================================================== -->
+  <!-- CALCULATE BUTTON                                                -->
+  <!-- Triggers the run() function which validates, computes, and     -->
+  <!-- renders the results.                                            -->
+  <!-- =============================================================== -->
   <button id="scd-btn"
     style="display:block;width:100%;padding:18px;background:#e66d00;color:#fff;font-size:20px;font-weight:700;border:none;border-radius:10px;cursor:pointer;margin-bottom:8px;letter-spacing:0.3px;">
     Calculate
   </button>
 
-  <!-- Error -->
+  <!-- =============================================================== -->
+  <!-- ERROR MESSAGE CONTAINER                                         -->
+  <!-- Hidden by default; shown by run() when validation fails.       -->
+  <!-- Uses warm orange/red palette to draw attention.                -->
+  <!-- =============================================================== -->
   <div id="scd-err" style="display:none;margin-top:20px;padding:16px 20px;background:#fff8f0;border:2px solid #c45500;border-radius:8px;font-size:16px;color:#3d1f00;line-height:1.7;"></div>
 
-  <!-- Results -->
+  <!-- =============================================================== -->
+  <!-- RESULTS SECTION                                                 -->
+  <!-- Hidden by default; revealed after a successful calculation.     -->
+  <!-- Contains: key-figure cards, security tier, tax note,            -->
+  <!-- year-by-year breakdown table, and contextual footnotes.         -->
+  <!-- =============================================================== -->
   <div id="scd-out" style="display:none;">
 
     <hr style="margin:36px 0;border:none;border-top:2px solid #d9d5cc;" />
@@ -140,92 +172,135 @@
 
 </div>
 
-<!-- Responsive override -->
+<!-- =================================================================== -->
+<!-- RESPONSIVE OVERRIDE                                               -->
+<!-- On screens wider than 480px (i.e. most phones in landscape or     -->
+<!-- larger), switch the four key-figure cards from a single column    -->
+<!-- to a two-column grid for better use of horizontal space.          -->
+<!-- =================================================================== -->
 <style>
 @media(min-width:480px){
   #scd-out>div:first-of-type{grid-template-columns:1fr 1fr !important;}
 }
 </style>
 
+<!-- =================================================================== -->
+<!-- JAVASCRIPT — CALCULATOR LOGIC                                     -->
+<!-- All computation, validation, and DOM manipulation lives inside    -->
+<!-- an IIFE to avoid polluting the global scope.                      -->
+<!-- =================================================================== -->
 <script>
 (function(){
+  /* ------------------------------------------------------------------ */
+  /*  g(n) — Format a number as GBP (e.g. 75000 → £75,000)             */
+  /*  Uses UK locale grouping with no decimal places for readability.   */
+  /* ------------------------------------------------------------------ */
   function g(n){return'\u00a3'+n.toLocaleString('en-GB',{minimumFractionDigits:0,maximumFractionDigits:0});}
 
+  /* ------------------------------------------------------------------ */
+  /*  run() — Main calculation entry point                              */
+  /*  1. Read & validate inputs                                         */
+  /*  2. Iterate year-by-year computing interest under the chosen model  */
+  /*  3. Populate summary cards (total, interest, annual, effective)     */
+  /*  4. Determine security tier from investment amount                  */
+  /*  5. Estimate UK tax at three marginal rates                         */
+  /*  6. Render the year-by-year breakdown table + totals row            */
+  /* ------------------------------------------------------------------ */
   function run(){
-    var a=parseFloat(document.getElementById('scd-amt').value),
-        r=parseFloat(document.getElementById('scd-rate').value),
-        t=parseInt(document.getElementById('scd-term').value),
-        mEl=document.querySelector('input[name="scd-m"]:checked'),
-        m=mEl?mEl.value:'cm',
-        e=document.getElementById('scd-err'),
-        o=document.getElementById('scd-out');
+    /* --- Read raw inputs --- */
+    var a=parseFloat(document.getElementById('scd-amt').value),      /* Investment amount (£) */
+        r=parseFloat(document.getElementById('scd-rate').value),     /* Annual interest rate (%) */
+        t=parseInt(document.getElementById('scd-term').value),       /* Bond term (years) */
+        mEl=document.querySelector('input[name="scd-m"]:checked'),  /* Selected payout method */
+        m=mEl?mEl.value:'cm',                                       /* Default to compound-at-maturity */
+        e=document.getElementById('scd-err'),                        /* Error container */
+        o=document.getElementById('scd-out');                        /* Results container */
+
+    /* --- Clear previous state --- */
     e.style.display='none';e.textContent='';o.style.display='none';
+
+    /* --- Input validation --- */
     if(isNaN(a)||a<20000){e.textContent='\u26a0 Minimum investment is \u00a320,000.';e.style.display='block';return;}
     if(isNaN(r)||r<0||r>3.5){e.textContent='\u26a0 Rate must be 0\u20133.5%.';e.style.display='block';return;}
     if(isNaN(t)||t<5){e.textContent='\u26a0 Minimum term is 5 years.';e.style.display='block';return;}
 
-    var cmp=m[0]==='c',ann=m[1]==='a',
-        bal=a,totI=0,totP=0,rows=[];
+    /* --- Decode method code --- */
+    /*  m[0] === 'c' → compound; 's' → simple                           */
+    /*  m[1] === 'a' → paid annually; 'm' → at maturity                 */
+    var cmp=m[0]==='c',                            /* compound? */
+        ann=m[1]==='a',                            /* annual payout? */
+        bal=a,                                     /* running balance for compound calc */
+        totI=0,                                    /* accumulated interest across all years */
+        totP=0,                                    /* accumulated payout across all years */
+        rows=[];                                   /* year-by-year data for the table */
 
+    /* --- Year-by-year interest computation --- */
     for(var y=1;y<=t;y++){
+      /* Interest for this year: compound uses running balance; simple always uses principal */
       var i=cmp?bal*(r/100):a*(r/100);
       totI+=i;
 
+      /* Payout: annual modes pay out each year; at-maturity pays everything in the final year */
       var p=0;
       if(ann){
-        /* Yearly payout: interest paid each year */
-        p=i;
-      }else if(y===t){
-        /* At-maturity: entire balance paid in final year */
-        p=cmp?bal+i:bal+i;
+        p=i;                                       /* yearly payout = this year's interest */
+      }else if(y===t){                              /* final year for at-maturity modes */
+        p=cmp?bal+i:bal+i;                          /* pay out current balance + final interest */
       }
       totP+=p;
 
-      /* Accumulate balance for compound modes */
+      /* Compound: add this year's interest to the running balance */
       if(cmp){
         bal+=i;
       }
 
       rows.push({
-        y:y,
-        i:i,
-        p:p,
-        /* Balance column: running balance before any payout */
-        cb:cmp?bal:(ann?a:bal)
+        y:y,                                        /* year number */
+        i:i,                                        /* interest earned in this year */
+        p:p,                                        /* amount paid out this year */
+        cb:cmp?bal:(ann?a:bal)                      /* closing balance displayed in table */
       });
     }
 
+    /* Simple at maturity: final balance is just the original principal */
     if(!cmp&&!ann) bal=a;
 
-    var total=ann?a+totP:(cmp?bal:a+totI),
-        netI=ann?totP:(cmp?bal-a:totI),
-        yrInc=ann?a*(r/100):netI/t,
-        eff=r===0?0:(ann?r:(Math.pow(total/a,1/t)-1)*100);
+    /* --- Summary calculations --- */
+    var total=ann?a+totP:(cmp?bal:a+totI),          /* total repayment to investor */
+        netI=ann?totP:(cmp?bal-a:totI),             /* net interest earned */
+        yrInc=ann?a*(r/100):netI/t,                  /* per-year income (actual or average) */
+        eff=r===0?0:(ann?r:(Math.pow(total/a,1/t)-1)*100);  /* effective annual rate (CAGR) */
 
+    /* --- Security tier based on investment amount --- */
     var sec=a<150000?'<strong>Unsecured</strong> \u2014 no legal charge (under \u00a3150,000)'
              :a<500000?'<strong>Tertiary charge</strong> \u2014 behind primary &amp; secondary (\u00a3150k\u2013\u00a3500k)'
              :'<strong>Secondary charge</strong> \u2014 behind primary mortgage only (over \u00a3500,000)',
         secBg=a<150000?'#fff8f0':a<500000?'#eaf2ec':'#eaf2ec',
         secBd=a<150000?'#c45500':a<500000?'#2d6a4f':'#2d6a4f';
 
+    /* --- Populate summary cards --- */
     document.getElementById('scd-r-total').textContent=g(total);
     document.getElementById('scd-r-interest').textContent=g(netI);
     document.getElementById('scd-r-annual').textContent=(ann?'':'~')+g(yrInc)+(ann?'/yr':'/yr avg');
     document.getElementById('scd-r-eff').textContent=eff.toFixed(2)+'%';
 
+    /* --- Update security tier display --- */
     var sb=document.getElementById('scd-r-sec');
     sb.style.background=secBg;sb.style.border='2px solid '+secBd;sb.style.color='#2d2d2d';
     document.getElementById('scd-r-sec-text').innerHTML=sec;
 
+    /* --- Estimate UK tax at three marginal rates --- */
+    /* Uses the annual income figure: actual for annual-payout modes, average for at-maturity. */
     var taxI=ann?yrInc:netI;
     document.getElementById('scd-r-tax').textContent='On '+g(taxI)+' interest: ~'+g(taxI*0.2)+' (basic), ~'+g(taxI*0.4)+' (higher), ~'+g(taxI*0.45)+' (additional rate) \u2014 before Personal Savings Allowance.';
 
+    /* --- Render year-by-year table --- */
     var tb=document.getElementById('scd-r-table');tb.innerHTML='';
     for(var j=0;j<rows.length;j++){
       var d=rows[j],
-          isFinal=(j===rows.length-1),
+          isFinal=(j===rows.length-1),               /* highlight the maturity row */
           tr=document.createElement('tr');
-      tr.style.background=isFinal?'#fff8f0':(j%2?'#f5f5f0':'#fff');
+      tr.style.background=isFinal?'#fff8f0':(j%2?'#f5f5f0':'#fff');  /* alternate row colours */
       tr.innerHTML='<td style="padding:10px 14px;border-bottom:1px solid #d9d5cc;color:#2d2d2d;font-weight:'+(isFinal?'700':'400')+';">'+d.y+(isFinal?' (maturity)':'')+'</td>'
         +'<td style="padding:10px 14px;border-bottom:1px solid #d9d5cc;text-align:right;font-family:monospace;color:#2d2d2d;">'+g(d.cb)+'</td>'
         +'<td style="padding:10px 14px;border-bottom:1px solid #d9d5cc;text-align:right;font-family:monospace;color:#2d2d2d;">'+g(d.i)+'</td>'
@@ -233,7 +308,7 @@
       tb.appendChild(tr);
     }
 
-    /* Add a totals row */
+    /* --- Totals row appended after the per-year rows --- */
     var ttr=document.createElement('tr');
     ttr.style.background='#f5f5f0';
     ttr.innerHTML='<td style="padding:10px 14px;border-top:2px solid #9a9a9a;font-weight:700;color:#2d2d2d;">Total</td>'
@@ -242,9 +317,14 @@
       +'<td style="padding:10px 14px;border-top:2px solid #9a9a9a;text-align:right;font-family:monospace;font-weight:700;color:#2d2d2d;">'+g(totP)+'</td>';
     tb.appendChild(ttr);
 
+    /* --- Reveal results section --- */
     o.style.display='block';
   }
 
+  /* ------------------------------------------------------------------ */
+  /*  Event binding — wire the Calculate button to run()               */
+  /*  Handles both synchronous (DOM already loaded) and async cases.    */
+  /* ------------------------------------------------------------------ */
   if(document.readyState==='loading'){
     document.addEventListener('DOMContentLoaded',function(){
       document.getElementById('scd-btn').addEventListener('click',run);