Compare electricity or gas plans to decide if you should lock in a rate or stay on a market tracker.
Consumption & Duration
Option A: Fixed Rate Plan
Option B: Variable Rate Plan
Estimate how much energy prices might rise or fall per year.
Cost Comparison (Over Months)
Total Cost (Fixed Rate):
Total Cost (Variable Rate):
Difference:
function calculateComparison() {
// 1. Get Inputs
var usage = parseFloat(document.getElementById('monthlyUsage').value);
var months = parseInt(document.getElementById('contractMonths').value);
var fixedUnit = parseFloat(document.getElementById('fixedUnitPrice').value);
var fixedFee = parseFloat(document.getElementById('fixedBaseFee').value);
var varUnit = parseFloat(document.getElementById('varStartPrice').value);
var varFee = parseFloat(document.getElementById('varBaseFee').value);
var trend = parseFloat(document.getElementById('marketTrend').value);
// Validation
if (isNaN(usage) || isNaN(months) || isNaN(fixedUnit) || isNaN(varUnit)) {
alert("Please enter valid numbers for usage, duration, and unit prices.");
return;
}
if (isNaN(fixedFee)) fixedFee = 0;
if (isNaN(varFee)) varFee = 0;
if (isNaN(trend)) trend = 0;
// 2. Calculate Fixed Cost
// Cost = (Usage * (Price/100)) + Fee
var monthlyFixedCost = (usage * (fixedUnit / 100)) + fixedFee;
var totalFixedCost = monthlyFixedCost * months;
// 3. Calculate Variable Cost
// We need to simulate the rate change month by month
var totalVariableCost = 0;
var currentVarUnit = varUnit;
// Calculate monthly compound rate for the trend
// Formula: (1 + annual_rate)^(1/12) – 1
var monthlyTrendFactor = Math.pow((1 + (trend / 100)), (1 / 12));
for (var i = 0; i < months; i++) {
// Calculate cost for this month
var monthlyCost = (usage * (currentVarUnit / 100)) + varFee;
totalVariableCost += monthlyCost;
// Update rate for next month based on trend
currentVarUnit = currentVarUnit * monthlyTrendFactor;
}
// 4. Display Results
document.getElementById('results-area').style.display = 'block';
document.getElementById('res-months').innerText = months;
document.getElementById('res-fixed-total').innerText = "$" + totalFixedCost.toFixed(2);
document.getElementById('res-var-total').innerText = "$" + totalVariableCost.toFixed(2);
var diff = Math.abs(totalFixedCost – totalVariableCost);
document.getElementById('res-diff').innerText = "$" + diff.toFixed(2);
// Verdict Logic
var verdictHTML = "";
if (totalFixedCost < totalVariableCost) {
verdictHTML = "Recommendation: Lock in the Fixed Rate.Even with the starting variable rate, the predicted market increases make the fixed plan cheaper by approximately $" + diff.toFixed(2) + " over the contract term.";
} else {
verdictHTML = "Recommendation: Choose the Variable Rate.Based on your market prediction, staying on the variable plan could save you approximately $" + diff.toFixed(2) + ". The fixed rate premium is currently too high relative to expected price changes.";
}
if (diff < 10) {
verdictHTML = "Recommendation: Neutral.The cost difference is negligible ($" + diff.toFixed(2) + "). You might prefer the Fixed Rate for peace of mind regarding budget certainty.";
}
document.getElementById('res-verdict').innerHTML = verdictHTML;
}
Understanding Fixed vs. Variable Rate Energy Plans
In the volatile world of energy markets, choosing between a fixed rate tariff and a variable rate plan is one of the most significant financial decisions a household or business can make. This calculator helps you mathematically model the potential outcomes based on your consumption and market predictions, rather than relying on guesswork.
What is a Fixed Rate Tariff?
A Fixed Rate plan locks in the price you pay per unit of energy (kilowatt-hour or kWh) for a set period, typically 12, 24, or 36 months.
It acts as an insurance policy against rising energy prices.
Pros: Budget certainty. Your unit price will not change even if the global cost of fuel spikes.
Cons: Often comes with a higher initial unit price compared to variable rates (the "risk premium"). If market prices crash, you are stuck paying the higher rate until your contract ends.
What is a Variable Rate Tariff?
A Variable Rate (or standard variable tariff) fluctuates based on the wholesale market costs of energy. Prices can go up or down at any time, usually with a notification period from your supplier.
Pros: Flexibility. No exit fees usually apply. You benefit immediately if global energy prices fall.
Cons: Unpredictability. A sudden geopolitical event or supply shortage can cause your monthly bills to skyrocket without warning.
The Mathematics of the Choice
The decision isn't just about comparing the current price tags. It involves calculating the Break-Even Point. To do this accurately, you must consider three factors:
The Premium: How much more expensive is the Fixed Rate currently compared to the Variable Rate?
Usage Volume: High-consumption households risk more money on variable volatility than low-consumption users.
Market Sentiment: The "Predicted Annual Market Price Change" field in the calculator above allows you to factor in inflation. If experts predict energy prices will rise by 20% this year, a Fixed Rate that is currently 10% more expensive is actually a bargain.
How to Use This Calculator
To get the most accurate result, grab your latest utility bill and find your Unit Rate (in cents or pence per kWh) and your Standing Charge (daily or monthly access fee).
Enter your average monthly usage. If you don't know it, typical values are roughly:
Low User (Apartment): 150 – 250 kWh
Medium User (3-Bedroom House): 300 – 450 kWh
High User (Large Home/Electric Heating): 500+ kWh
Use the "Predicted Market Change" input to stress-test your decision. See what happens if prices rise by 5%, 10%, or even 20% to see if the Fixed Rate still offers value.