The tax benefits of marriage and civil partnership in the UK are something a lot of couples genuinely don’t think about until it’s too late to use them — or, in some cases, until a bereavement makes the difference painfully obvious. This isn’t really about whether marriage is the “right” choice for any particular couple — that’s a personal decision, and the UK tax system shouldn’t be the deciding factor in it. But the reality is that the number of cohabiting couples in the UK has grown by around 144% since 1996, from roughly 1.5 million to about 3.6 million, and a meaningful share of those couples are, often unknowingly, leaving genuinely significant tax advantages on the table simply because they’ve never been formally pointed out.
This guide walks through what those benefits actually are, how much they’re realistically worth, and — just as importantly — what cohabiting couples can do to protect themselves given that the law treats them very differently, however long they’ve been together.
Quick Answer: Tax Benefits of Marriage vs Cohabitation in the UK
Married couples and civil partners in the UK have access to several tax advantages that cohabiting couples do not, regardless of how long they’ve lived together. The main ones are: the Marriage Allowance, worth up to £252 a year for 2026/27 if one partner earns below the personal allowance; Capital Gains Tax-free transfers between spouses, allowing both partners’ £3,000 annual exemptions to be used; and, by far the largest in practice, an unlimited Inheritance Tax exemption on assets passed to a spouse or civil partner, plus the ability to combine unused nil-rate bands — worth up to £650,000 tax-free between a married couple, compared with just £325,000 for an unmarried partner, above which 40% IHT applies. Cohabiting couples can replicate some of the practical effects through careful planning — wills, trusts, and joint ownership structures — but none of this happens automatically the way it does for married couples, and gaps in planning can be expensive.
The Marriage Allowance: Small, But Genuinely Free Money
The Marriage Allowance lets a lower-earning spouse or civil partner transfer £1,260 of their unused personal allowance to their partner, provided the receiving partner is a basic-rate taxpayer. For 2026/27, this transfer is worth up to £252 a year — the £1,260 transferred, taxed at the recipient’s 20% basic rate, equals £252 saved.
The eligibility conditions are fairly specific: the partner giving up the allowance must have income below the personal allowance (£12,570 for 2026/27), and the partner receiving it must be a basic-rate taxpayer — if either partner is a higher or additional rate taxpayer, the allowance doesn’t apply. This commonly fits couples where one partner works part-time, is on maternity or paternity leave, is a full-time student, or isn’t working at all, while the other is in steady basic-rate employment.
Also Read: How the Personal Allowance and Income Tax Operate
What makes this genuinely worth checking is that once claimed, it carries forward automatically into future tax years until cancelled or until circumstances change — so a couple who become eligible and claim it once don’t need to reapply annually. It can also be backdated up to four years, meaning couples who were eligible in previous years but never claimed can potentially receive a lump sum covering multiple years at once. £252 a year might not transform anyone’s finances on its own, but combined with backdating, it can mean over £1,000 landing as a one-off payment for a couple who simply never knew to apply.
It’s worth distinguishing this from the separate, much more limited Married Couple’s Allowance, which is worth up to £1,170 for 2026/27 but is only available where one partner was born before 6 April 1935 — meaning, practically, it applies to a very small and shrinking number of couples. The Marriage Allowance is the one relevant to almost everyone; the Married Couple’s Allowance is a historical leftover relevant to almost no one under current rules.
Capital Gains Tax: Doubling Up on Allowances
This is one of the more genuinely useful — if less headline-grabbing — benefits, and it ties into something covered in more detail elsewhere on this site: transfers of assets between spouses and civil partners are completely exempt from Capital Gains Tax, treated as a “no gain, no loss” transfer regardless of how much the asset has increased in value.
With the CGT Annual Exempt Amount now down to just £3,000 per person for 2026/27 (a steep fall from £12,300 just a few years ago, as covered in our guide to Capital Gains Tax), the practical value of this has shrunk somewhat — but it hasn’t disappeared. A married couple can, between them, realise up to £6,000 in gains tax-free each year by transferring part of an asset to whichever partner has unused allowance before a sale, compared with just £3,000 for an individual or unmarried partner.
There’s also a rate benefit: if one partner is a basic-rate taxpayer and the other is higher-rate, transferring an asset to the lower-earning partner before selling means the gain is taxed at 18% rather than 24% — a straightforward, entirely legal way to reduce the tax on a gain simply by ensuring it’s realised by the partner in the lower tax band. For cohabiting couples, any such transfer is treated as a disposal in its own right — potentially triggering CGT on the transfer itself, which can undermine the whole point of the exercise.
Inheritance Tax: Where the Real Money Is
If there’s one section of this article worth reading carefully regardless of how the rest applies to you, it’s this one — because Inheritance Tax is where the gap between married and cohabiting couples is largest, and where the consequences of not planning are most severe.
The Spousal Exemption: Unlimited, Automatic
Assets left to a spouse or civil partner on death are completely exempt from Inheritance Tax, with no upper limit. This applies automatically — there’s no claim to make, no form to fill in beyond the normal probate process. A surviving spouse can inherit an estate worth £2 million, £5 million, or more, entirely free of IHT, simply by virtue of being a spouse.
For cohabiting couples, this exemption simply doesn’t exist. Anything left to a cohabiting partner above the standard £325,000 nil-rate band is potentially subject to 40% Inheritance Tax — the same rate that would apply to a gift to a distant relative or even an unrelated friend. For a couple who’ve lived together for twenty years, built a life and a home together, but never married, this can mean a genuinely shocking tax bill at exactly the point when the surviving partner is least equipped to deal with it.
Combining Nil-Rate Bands
Beyond the spousal exemption itself, married couples and civil partners benefit from being able to transfer any unused portion of the £325,000 nil-rate band to the surviving partner. In practice, this means that when the second spouse dies, their estate can potentially have up to £650,000 of nil-rate band available — double the individual amount — before the standard 40% rate applies (with the residence nil-rate band potentially adding further tax-free allowance on top for those leaving a home to direct descendants).
Cohabiting couples have no equivalent mechanism. Each partner’s £325,000 nil-rate band exists individually, but there’s no transfer between them — because there’s no spousal exemption to leave unused in the first place.
The April 2026 Business and Agricultural Relief Changes
This is a genuinely current development worth flagging. Changes to Business Relief and Agricultural Property Relief, taking effect from April 2026, introduce an additional £1 million IHT-free allowance per person for certain qualifying business and agricultural assets. For married couples, this creates a new planning opportunity: because assets can move between spouses free of IHT and CGT during their lifetimes, it may be possible to structure ownership so that each partner individually qualifies for their own £1 million allowance — potentially doubling the relief available to a couple, where a single unmarried owner would only access it once.
For unmarried couples who jointly run a business or own agricultural assets together, this route is either blocked or severely limited, because the tax-free restructuring that makes it possible for spouses simply isn’t available. If this applies to your situation — a family business or farm, for example — this is genuinely worth raising with an accountant specifically in light of the 2026 changes, regardless of which side of the marriage question you sit on.
ISAs: The Combined Allowance and What Happens on Death
Every UK adult has their own £20,000 annual ISA allowance, regardless of marital status — so a couple, married or not, can between them shelter £40,000 a year from tax. Where marriage makes a difference is in moving money between ISAs: because transfers between spouses are CGT-exempt and IHT-exempt, a married couple can rebalance who holds what — moving investments from one partner’s ISA to the other’s via a sale and repurchase, for example — without the tax friction that would apply to a similar rearrangement between unmarried partners.
There’s also a specific and valuable benefit on death: a surviving spouse or civil partner can claim an Additional Permitted Subscription (APS), which allows them to effectively inherit their late partner’s ISA allowance — adding an amount equal to the value of the deceased’s ISA to their own ISA allowance, on top of their normal annual limit. This preserves the tax-free status of those savings within the household. Cohabiting partners have no equivalent right — an ISA held by a deceased cohabiting partner simply forms part of their estate like any other asset, with no special allowance passed to the survivor.
What Cohabiting Couples Can Actually Do
None of this is to say cohabiting couples are without options — but unlike married couples, almost nothing happens automatically, which means deliberate planning matters considerably more.
Write a will — and keep it updated. Without a will, intestacy rules apply on death, and cohabiting partners have no automatic entitlement under intestacy regardless of how long the relationship has lasted. A will is the single most important step, and it costs a fraction of what an unplanned-for IHT bill would.
Consider a trust for larger assets, particularly property. Trust structures can, in some circumstances, help manage how jointly-held property passes between cohabiting partners — though this is genuinely an area where professional legal advice matters, as the rules are detailed and mistakes can be costly.
Use life insurance written in trust to cover a potential IHT liability. If a significant IHT bill on the family home is a realistic prospect for a cohabiting couple, a life insurance policy specifically structured to pay out to cover that bill — written in trust so the payout itself doesn’t add to the taxable estate — is a commonly used, practical mitigation.
Get a cohabitation agreement. While this doesn’t directly change tax treatment, it clarifies ownership shares and intentions — which becomes important when working out what’s actually in each partner’s estate for IHT purposes, and can prevent disputes alongside the tax planning itself.
For the official guidance on claiming the Marriage Allowance, including the backdating process, GOV.UK’s Marriage Allowance page sets out the eligibility criteria and application process directly. For a clear breakdown of how the Inheritance Tax spousal exemption and nil-rate band transfer work, GOV.UK’s guidance on Inheritance Tax for married couples and civil partners is the authoritative source. And for cohabiting couples specifically, Citizens Advice’s guide to cohabitation and the law explains what rights do — and don’t — exist, and is a sensible starting point before seeking tailored legal advice.
A Quick Comparison
| Benefit | Married / Civil Partners | Cohabiting Couples |
| Marriage Allowance | Up to £252/year, backdatable 4 years | Not available |
| CGT on asset transfers between partners | Exempt (no gain, no loss) | Treated as a disposal — may trigger CGT |
| IHT on assets left to partner | Unlimited spousal exemption | £325,000 nil-rate band, then 40% |
| Combined IHT nil-rate band | Up to £650,000 (transferable) | £325,000 each, not transferable |
| ISA allowance on death (APS) | Survivor inherits deceased’s ISA allowance | No equivalent right |
| Intestacy rights (no will) | Automatic entitlement under intestacy rules | No automatic entitlement, regardless of duration |
Frequently Asked Questions
How much is the Marriage Allowance worth in 2026/27?
The Marriage Allowance is worth up to £252 for the 2026/27 tax year, allowing a lower-earning spouse or civil partner to transfer £1,260 of their unused personal allowance to a basic-rate taxpaying partner. It can also be backdated up to four years if the couple was eligible but never claimed, potentially resulting in a lump-sum payment of over £1,000.
Do cohabiting couples get any of the same tax benefits as married couples?
Generally, no. The Marriage Allowance, the Inheritance Tax spousal exemption, transferable nil-rate bands, CGT-exempt transfers between partners, and the ISA Additional Permitted Subscription on death are all unavailable to cohabiting couples, regardless of how long they’ve lived together. Cohabiting couples can replicate some practical outcomes through wills, trusts, and life insurance, but none of it happens automatically.
How much Inheritance Tax could a cohabiting couple pay compared to a married couple?
A married couple can pass an unlimited amount to each other on death with no Inheritance Tax at all, and can combine their nil-rate bands for up to £650,000 tax-free when the second partner dies. A cohabiting partner inheriting from their partner only has the standard £325,000 nil-rate band, with 40% IHT charged on anything above that — which on a family home in many parts of the UK can mean a tax bill running into tens or even hundreds of thousands of pounds.
Can cohabiting couples avoid Capital Gains Tax when transferring assets to each other?
No — unlike married couples and civil partners, who can transfer assets to each other on a “no gain, no loss” basis with no CGT, a transfer of an asset between cohabiting partners is treated as a disposal for CGT purposes and may trigger a tax charge if the asset has increased in value, even though no money may have changed hands.
What’s the single most important step for an unmarried couple to protect themselves?
Writing a will is generally considered the most important and most commonly overlooked step. Without one, intestacy rules apply on death, and a cohabiting partner — regardless of the length or seriousness of the relationship — has no automatic legal entitlement to the deceased partner’s estate. A will, combined with appropriate life insurance and clear agreements about jointly-owned assets, addresses the areas where cohabiting couples are most exposed.
Conclusion
The hidden tax benefits of marriage and civil partnership in the UK aren’t really hidden in the sense of being secret — they’re written into tax law and freely available to anyone who qualifies. What’s hidden is awareness: a huge number of couples, married and cohabiting alike, simply don’t know these benefits exist, don’t know they might be eligible, or don’t realise quite how large the gap becomes — particularly around Inheritance Tax — until a life event forces the question.
Also Read: How to Navigate UK Inheritance Tax: Tips for Protecting Your Wealth
For married couples and civil partners, checking eligibility for the Marriage Allowance costs nothing and takes minutes, and understanding how the IHT spousal exemption and nil-rate band transfer work is worth doing well before it becomes urgent. For cohabiting couples, the message is less about what the tax system offers and more about what it doesn’t — and the practical response, regardless of any couple’s views on marriage itself, is the same: a will, clarity about ownership, and proper planning around the assets that matter most. None of this needs to be done all at once, but all of it is considerably easier to address now than after the fact.
Disclaimer: This article is for informational purposes only and does not constitute tax, financial, or legal advice. Tax allowances, thresholds, and rules referenced are correct as of the 2026/27 tax year but are subject to change, and individual circumstances vary considerably. Always consult a qualified accountant, solicitor, or financial adviser for advice specific to your situation, particularly regarding wills, Inheritance Tax planning, and cohabitation arrangements.
