.mrr-calc-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e1e1e1;
border-radius: 8px;
background-color: #f9f9f9;
color: #333;
}
.mrr-calc-header {
text-align: center;
margin-bottom: 30px;
}
.mrr-calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.mrr-input-group {
margin-bottom: 15px;
}
.mrr-input-group label {
display: block;
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
}
.mrr-input-group input {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
font-size: 16px;
}
.mrr-calc-btn {
grid-column: span 2;
background-color: #005ea5;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
transition: background 0.3s;
margin-top: 10px;
}
.mrr-calc-btn:hover {
background-color: #004a87;
}
.mrr-results {
margin-top: 30px;
padding: 20px;
background-color: #fff;
border: 2px solid #005ea5;
border-radius: 6px;
display: none;
}
.mrr-result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.mrr-result-row:last-child {
border-bottom: none;
}
.mrr-result-label {
font-weight: 600;
}
.mrr-result-value {
font-family: monospace;
font-size: 1.1em;
font-weight: bold;
}
.mrr-info-section {
margin-top: 40px;
line-height: 1.6;
}
.mrr-info-section h2 {
color: #005ea5;
border-bottom: 2px solid #005ea5;
padding-bottom: 10px;
}
.mrr-info-section h3 {
margin-top: 25px;
}
@media (max-width: 600px) {
.mrr-calc-grid {
grid-template-columns: 1fr;
}
.mrr-calc-btn {
grid-column: span 1;
}
}
Taxable Profits (£)
Exempt Distributions/Dividends (£)
Number of Associated Companies
Days in Accounting Period
Calculate Tax Liability
Augmented Profits:
£0.00
Tax at Main Rate (25%):
£0.00
Marginal Relief Amount:
-£0.00
Net Corporation Tax Payable:
£0.00
Effective Tax Rate:
0%
Understanding Marginal Rate Relief
From 1 April 2023, the UK Corporation Tax rates changed. Companies with taxable profits below £50,000 pay the Small Profits Rate of 19% . Companies with profits above £250,000 pay the Main Rate of 25% .
Marginal Rate Relief provides a gradual increase in the tax rate for companies with profits between these two thresholds, ensuring there isn't a sudden "cliff edge" tax hike.
How is Marginal Relief Calculated?
The calculation uses a "standard fraction" (currently 3/200). The formula applied is:
Relief = (Upper Limit – Augmented Profits) × (3/200) × (Taxable Profit / Augmented Profit)
Key Definitions
Augmented Profits: The sum of your taxable profits plus any exempt distributions (dividends) received from non-group companies.Associated Companies: Companies are associated if one controls the other or both are under the control of the same person(s). Having associated companies reduces your Upper and Lower limit thresholds proportionally.Limits: The £50,000 and £250,000 limits are adjusted (apportioned) if your accounting period is shorter than 12 months or if you have associated companies.
Example Scenario
If a single company has £150,000 in taxable profit and no associated companies:
Tax at Main Rate (25%): £37,500
Relief calculation: (£250,000 – £150,000) × 3/200 = £1,500
Net Tax: £37,500 – £1,500 = £36,000
Effective Rate: 24%
function calculateMarginalRelief() {
var taxableProfit = parseFloat(document.getElementById('taxableProfit').value);
var exemptDistributions = parseFloat(document.getElementById('exemptDistributions').value) || 0;
var associatedCompanies = parseInt(document.getElementById('associatedCompanies').value) || 0;
var periodDays = parseInt(document.getElementById('periodDays').value) || 365;
if (isNaN(taxableProfit) || taxableProfit < 0) {
alert("Please enter a valid taxable profit amount.");
return;
}
var resultsBox = document.getElementById('mrrResultsBox');
var resAugmented = document.getElementById('resAugmented');
var resMainRate = document.getElementById('resMainRate');
var resRelief = document.getElementById('resRelief');
var resNetTax = document.getElementById('resNetTax');
var resEffectiveRate = document.getElementById('resEffectiveRate');
// Thresholds
var baseLowerLimit = 50000;
var baseUpperLimit = 250000;
var standardFraction = 3/200; // 0.015
// Adjust limits for associated companies and period length
var divisor = associatedCompanies + 1;
var timeFactor = periodDays / 365;
var adjustedLowerLimit = (baseLowerLimit / divisor) * timeFactor;
var adjustedUpperLimit = (baseUpperLimit / divisor) * timeFactor;
var augmentedProfits = taxableProfit + exemptDistributions;
var mainRateTax = taxableProfit * 0.25;
var reliefAmount = 0;
var finalTax = 0;
if (augmentedProfits = adjustedUpperLimit) {
// Pay Main Rate (25%)
finalTax = mainRateTax;
reliefAmount = 0;
} else {
// Marginal Relief applies
// Formula: (Upper Limit – Augmented Profits) * Fraction * (Taxable / Augmented)
var rangeReduction = adjustedUpperLimit – augmentedProfits;
var profitRatio = (augmentedProfits === 0) ? 1 : (taxableProfit / augmentedProfits);
reliefAmount = rangeReduction * standardFraction * profitRatio;
finalTax = mainRateTax – reliefAmount;
}
// Catch edge cases where math might result in negative tax
if (finalTax 0) ? (finalTax / taxableProfit) * 100 : 0;
// Display results
resAugmented.innerText = "£" + augmentedProfits.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resMainRate.innerText = "£" + mainRateTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resRelief.innerText = "-£" + reliefAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resNetTax.innerText = "£" + finalTax.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resEffectiveRate.innerText = effectiveRate.toFixed(2) + "%";
resultsBox.style.display = 'block';
}