How D1 works mechanically
D1 is the additional-rate flat-rate code:
- No personal allowance applied
- All income from this source taxed at 45%
- Used when your overall income exceeds £125,140
For a £30,000 second job with D1: - £30,000 × 45% = £13,500 Income Tax - Plus 2% NI (above upper limit): £600 - Net: £15,900
The same £30,000 on 1257L (if it were your only job): - £30,000 − £12,570 allowance = £17,430 taxable - £17,430 × 20% = £3,486 Income Tax
D1 wrongly applied to a sole £30,000 job costs the worker £10,014 extra per year.
When D1 is correct
D1 is right when:
- Your main job earns enough to exceed £125,140 (additional-rate threshold for 2026/27)
- A secondary income source exists (second employment, pension, occasionally rental income that's PAYE-collected)
- HMRC's view: every pound from the secondary source is in additional-rate territory
Example: - Main job: £150,000 (1257L or T-suffix code, personal allowance fully tapered) - Second pension: £20,000 (D1) - Total: £170,000; the £20k secondary is all in additional-rate territory
When D1 is wrong
D1 is wrong if:
- It's on your sole income source — even at high earnings, the bands below £125,140 should apply
- Your total income hasn't reached £125,140 — at any lower income, D1 over-deducts
- A pay structure change has reduced your earnings but the code hasn't updated
If you suspect D1 is wrong, check your HMRC Personal Tax Account first — the calculation behind the code is visible there.
D0 vs D1 — practical comparison
| Income range total | Likely main code | Likely secondary-source code |
|---|---|---|
| Below £50,270 | 1257L | 1257L (split) or BR |
| £50,270 – £100,000 | 1257L | BR or D0 |
| £100,000 – £125,140 | T-suffix code (tapering allowance) | D0 |
| Above £125,140 | T-suffix or 0T (allowance fully tapered) | D1 |
The threshold where D0 transitions to D1 on a secondary source is £125,140 total income.
The 60% trap interaction
Between £100,000 and £125,140, the personal allowance tapers (lose £1 of allowance for every £2 of income above £100k). The effective marginal rate in this band is 62% (40% + 20% allowance loss + 2% NI = 62%).
D1 doesn't apply in this band — it kicks in above £125,140. But if you're earning into the £100k–£125,140 range, the main job's code typically becomes a tailored T-suffix code rather than 1257L, and any secondary source might get D0 then D1 as total income rises.
Read more about £100k tax planning →
How to fix D1 if wrong
- Log in to your HMRC Personal Tax Account
- Verify your main vs secondary income is set correctly
- Confirm total expected annual income
- HMRC reissues the correct code typically within 2-6 weeks
- PAYE refunds overpayment automatically through subsequent pay periods
If urgent (e.g. D1 is on a £30,000 sole job), call HMRC directly on 0300 200 3300 — escalated cases can be resolved within days.
In short
Tax code D1 taxes every pound from this income source at the additional rate of 45%. Right for secondary income when your main job already exceeds £125,140; wrong on your sole income. Affects only the top few percent of UK earners. For the broader tax code reference, see the tax codes hub →. To verify your specific code, use the tax code checker →.