Percentage Calculator
Calculate percentages in multiple ways — find percentage of a number, percentage change, or what percent one number is of another.
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function switchTab(id,btn){document.querySelectorAll('.calc-panel').forEach(p=>p.classList.remove('active'));document.querySelectorAll('.tab-btn').forEach(b=>b.classList.remove('active'));document.getElementById('panel-'+id).classList.add('active');btn.classList.add('active');}
function calcPctOf(){const p=+document.getElementById('p1-pct').value,n=+document.getElementById('p1-num').value;if(!p||!n){alert('Fill both fields');return;}const r=((p/100)*n);document.getElementById('r1-val').textContent=r%1===0?r:r.toFixed(2);document.getElementById('r1-lbl').textContent=p+'% of '+n+' = '+r.toFixed(2);document.getElementById('r1').style.display='block';}
function calcWhatPct(){const x=+document.getElementById('p2-x').value,y=+document.getElementById('p2-y').value;if(!x||!y){alert('Fill both fields');return;}const r=((x/y)*100).toFixed(2);document.getElementById('r2-val').textContent=r+'%';document.getElementById('r2-lbl').textContent=x+' is '+r+'% of '+y;document.getElementById('r2').style.display='block';}
function calcPctChange(){const o=+document.getElementById('p3-old').value,n=+document.getElementById('p3-new').value;if(!o){alert('Fill both fields');return;}const c=((n-o)/Math.abs(o)*100).toFixed(2);const inc=n>=o;document.getElementById('r3-val').textContent=(inc?'+':'')+c+'%';document.getElementById('r3-val').style.color=inc?'#16a34a':'#dc2626';document.getElementById('r3-lbl').textContent=(inc?'Increase':'Decrease')+' from '+o+' to '+n;document.getElementById('r3').style.display='block';}
function calcAddRemove(){const n=+document.getElementById('p4-num').value,p=+document.getElementById('p4-pct').value;if(!n||!p){alert('Fill both fields');return;}document.getElementById('r4-add').textContent=(n*(1+p/100)).toFixed(2);document.getElementById('r4-rem').textContent=(n*(1-p/100)).toFixed(2);document.getElementById('r4-diff').textContent=(n*p/100).toFixed(2);document.getElementById('r4').style.display='block';}
document.addEventListener('DOMContentLoaded',()=>{document.getElementById('related-grid').innerHTML=TOOLS.filter(t=>t.category==='grade'&&t.slug!=='percentage-calculator').slice(0,4).map(buildToolCard).join('');});