Tax Code Checker Guide UK 2026 — Common Mistakes & How to Fix Them

Your tax code determines how much tax you pay. Get it wrong and you could be overpaying — or face an unexpected bill. Here’s how to check yours.

Understanding Tax Codes

Common Tax Codes Explained

Code	Meaning	Who Has It
1257L	Standard code — £12,570 allowance	Most employees
BR	Basic Rate — all income taxed at 20%	Second job (usually)
D0	Higher Rate — all taxed at 40%	Second job (high earner)
D1	Additional Rate — all taxed at 45%	Very high earners
NT	No Tax	Certain circumstances
0T	No allowances	Allowances used elsewhere
K	You owe extra	Benefits, reduced allowances
S	Scottish taxpayer	Lives in Scotland
C	Welsh taxpayer	Lives in Wales

Breaking Down the Code

1257L Explained:

Part	Meaning
1257	£12,570 allowance (multiply by 10)
L	Standard Personal Allowance applies

Other Letters:

Letter	Meaning
L	Standard Personal Allowance
M	Marriage Allowance received
N	Marriage Allowance transferred
T	HMRC reviewing your code
W1/M1	Emergency — non-cumulative
X	Special circumstances

Is Your Code Correct?

Quick Check

Your Situation	Expected Code
Single job, standard circumstances	1257L
Receiving Marriage Allowance	1383L or similar
Transferring Marriage Allowance	1194N
Two jobs	1257L (main) + BR (second)
Company benefits (car, health)	Lower number (e.g., 1100L)
State Pension + job	Reduced number
Student loan	No effect on code

Warning Signs of Wrong Code

Sign	What It Means
Sudden pay decrease	Code may have changed incorrectly
Tax code letter is 0T	No allowances — check why
W1 or M1 suffix	Emergency code — needs sorting
K code unexpectedly	May be wrong
Different to colleagues (same job)	One of you is wrong

Common Tax Code Errors

Error 1: Benefits Not Removed

Problem	Effect
Left old job with company car	Still taxed as if you have it
Private healthcare ended	Still reducing your allowance
Fix	Report change to HMRC immediately

Error 2: Two Jobs, Wrong Allocation

Problem	Effect
Both jobs have BR code	Overpaying tax
Personal Allowance split wrong	Could be overpaying
Changed main job, code not updated	Wrong allocation
Fix	Update HMRC which is your main job

Error 3: Marriage Allowance Not Applied

Problem	Effect
Applied but not on code	Missing £252/year
Applied to wrong partner	No benefit
Fix	Check gov.uk/marriage-allowance

Error 4: Emergency Tax Code

Problem	Effect
New job, emergency code	May overtax initially
Shows W1/M1/X suffix	Non-cumulative calculation
Fix	Provide P45 or complete starter checklist

Error 5: Wrong Address (Scotland/Wales)

Problem	Effect
HMRC thinks you’re in Scotland	S code applied
Scottish rates different	May be wrong tax
Fix	Update address with HMRC

How to Check Your Tax Code

Method 1: Personal Tax Account

Step	Action
1	Go to gov.uk/personal-tax-account
2	Sign in with Government Gateway
3	View your tax code
4	See what’s included in calculation
5	Report if incorrect

Method 2: Check Your Payslip

Look For	Should Show
Tax code	Your current code
Tax paid this period	Amount deducted
Tax paid year to date	Cumulative
NI paid	Separate line

Method 3: P60 (End of Year)

Document	Shows
P60	Annual earnings and tax paid
Available	After April 5
Keep	For 22 months minimum

Getting Refunds

How Much Could You Be Owed?

Error Type	Typical Overpayment
Wrong code for 1 year	£500-2,000
Wrong code for 4 years	£2,000-8,000
Emergency tax on new job	£100-500
Old benefits still on code	£500-2,000

Claiming Back Overpaid Tax

Method	When to Use
Automatic refund	HMRC updates code mid-year
P800 letter	HMRC sends after year-end
Form P87	Simple expense claims
Self Assessment	Complex situations

Timeline for Refunds

Claim For	Deadline
2025/26	April 2030
2024/25	April 2029
2023/24	April 2028
2022/23	April 2027

You can claim refunds for the previous 4 complete tax years.

What Affects Your Tax Code

Things That Reduce Your Allowance

Factor	Effect on Code
Company car	Lower number
Private medical insurance	Lower number
Living accommodation	Lower number
Income over £100k	Lose allowance
Underpaid tax from previous year	Lower number
State Pension	Lower number (if employed too)

Things That Increase Your Allowance

Factor	Effect on Code
Marriage Allowance received	Higher number (M suffix)
Blind person’s allowance	Higher number
Job expenses (if claimed)	Higher number

Income Over £100,000

Income	Personal Allowance	Code
£100,000	£12,570	1257L
£110,000	£7,570	757L
£120,000	£2,570	257L
£125,140+	£0	0T

Lose £1 of allowance for every £2 over £100,000.

Special Situations

Multiple Jobs

Approach	How It Works
Full allowance on main job	1257L
No allowance on second job	BR or D0
Split allowance	Partial on each

State Pension + Employed

How It Works
State Pension uses some allowance	Reduces your code
Example: £9,000 State Pension	Code might be 357L
You effectively pay tax on State Pension	Via your employment

Company Car

Car List Price	CO2 Impact	Rough Allowance Reduction
£30,000	Medium	~£8,000 from allowance
£30,000	Electric (3%)	~£900 from allowance

Electric cars have minimal impact on your tax code.

Taking Action

If Your Code Is Wrong

Step	Timeframe
Check Personal Tax Account	Now
Gather evidence (payslips, P60)	Before contacting
Call HMRC (0300 200 3300)	Allow 30+ mins
Or update online	Usually quicker
Wait for new coding notice	2-6 weeks
Check refund arrives	Next paycheck or P800

What to Tell HMRC

Information Needed	Why
Your NI number	Identifies you
Current tax code	What you’re querying
What’s wrong	Specific issue
Evidence	P45, payslips, etc.

Key Takeaways

1. 1257L is standard — most people should have this
2. Check annually — codes can go wrong any time
3. Use Personal Tax Account — easiest way to check
4. Report changes — company car, job change, etc.
5. Claim refunds — up to 4 years back
6. £100k+ income — expect reduced allowance

For related content, see our take-home pay calculator, marriage allowance guide, and income tax guide.