How to fill in form C4 — correcting an Inheritance Tax account
Form C4 is the HMRC form personal representatives use to correct an Inheritance Tax account (almost always IHT400) after it has already been submitted — telling HMRC that the estate paid too much or too little tax, with corrected figures, within six months of discovering the error.
It is not the form for a loss-on-sale refund — that's IHT35 for shares or IHT38 for land — and every accountable person who signed the original account must sign C4 personally; HMRC will not accept it from an agent.
This walkthrough takes C4 box by box: the four totals that work out the net change, the tax-calculation boxes you can safely leave blank, and the signing rule that catches more estates out than the arithmetic does.
✓ Updated 2026 · verified against GOV.UK
In design
United Kingdom·Informational, not legal or financial advice·Verified against GOV.UK, 2026
This walkthrough takes the C4 form field by field, in plain English. Most of it is administrative — the difficulty is knowing which boxes actually matter, and the one most families get wrong.
The thing most people get wrong
Box 8 (decreases in liabilities, exemptions or reliefs) and box 11 (increases in liabilities, exemptions or reliefs) work in the OPPOSITE direction to the one their headings suggest.
A liability going DOWN, or an exemption going down, makes the estate MORE valuable for tax purposes — so box 8 adds to the total increase (box 9), not the total decrease.
Get this backwards and every figure below it is wrong.
The form, in summary
Valoren
C4·3 pages·17 fields guided
With Valoren30–40 minutes
with the original IHT400 figures already in the file
Without Valoren2–4 hours
reconciling the change against the original IHT400 schedules
Form C4 is the mechanism for section 217 of the Inheritance Tax Act 1984: if a person who delivered an account under section 216 (almost always IHT400) later discovers it is defective in a material respect, they must deliver a further account — C4 — within six months of that discovery.
The deadline runs from discovery, not from the date of death or the date the original account was filed, and it applies whether the correction increases or decreases the tax due.
C4 has no role for a value change caused by a post-death sale of shares or land — those go on IHT35 or IHT38 — and it has no role for a change to a transferable nil-rate band claim, which HMRC asks to be raised by letter or on IHT402 instead.
·Who Files — Every person who delivered the original IHT400 account, signing personally — HMRC will not accept a C4 signed by an agent
·3 pages · 17 fields guided
·Draws from your Estate File — Legal Instruments, Property Folio, Financial Accounts
Section01
§11
Section 1
Before you file — is C4 the right form?
Form C4 has one job: telling HMRC that a previously delivered Inheritance Tax account was wrong, in either direction. It's easy to reach for it in situations another form actually covers — check the list below before you start.
01
What C4 actually corrects
C4 amends an Inheritance Tax account already delivered to HMRC under section 216 of the Inheritance Tax Act 1984 — in practice, almost always IHT400.
It covers a value that turns out to be wrong, a liability, exemption or relief that was missed or changed, or an asset that was left off the original account entirely.
It has no role if IHT400 hasn't been filed yet — amend the account itself before delivery, not with C4.
02
Not for a loss-on-sale refund
The C4 form itself says this explicitly: you cannot use it to claim a reduction to land and buildings, or to stocks and shares, that results from a sale.
Sold a house for less than its probate value? Use IHT38.
Sold quoted shares for less than their probate value? Use IHT35.
HMRC will not process a loss-on-sale claim made through C4 — it has to go on the dedicated form.
03
Not for a transferable nil-rate band change
C4 does not cover a change to the amount of transferable nil-rate band available from an earlier death.
HMRC's own guidance on the form says to write to them directly, explaining what has changed — this is a letter, not a C4 filing.
A transferable nil-rate band claim itself is made on form IHT402 (already covered on Valoren).
04
The six-month deadline — and what it counts from
Section 217 of the Inheritance Tax Act 1984 gives you six months to deliver a corrective account once you discover the original one is defective.
The clock starts on discovery — not on the date of death, and not on the date IHT400 was originally filed.
A correction found five years after probate still has to be made within six months of finding it.
05
Running out of room
If there isn't enough space on C4 itself, use form C4(C) — the continuation page — rather than starting a second C4.
Scotland has its own version, C4(S), which does a second job on top of correcting HMRC's figures: it's also the mechanism for adding assets to a Grant of Confirmation through the Sheriff Court. C4(S) is not simply the Scottish translation of C4 — don't substitute one for the other.
Form C4 has one job: telling HMRC that a previously delivered Inheritance Tax account was wrong, in either direction. It's easy to reach for it in situations another form actually covers — check the list below before you start.
HM Revenue & Customs (HMRC) · C4❦
Section02
§22
Section 2
Boxes 1–6: identifying the estate and the account you're correcting
The top of C4 establishes which estate and which original account you're amending. HMRC cross-checks these details against the IHT400 already on file, so they need to match exactly.
01
Boxes 1–3 — deceased's name, IHT reference, date of death
Name and date of death as they appear on the original IHT400.
The Inheritance Tax reference (box 2) is the one HMRC issued when the original account was processed — it's on their acknowledgement letter, and usually on any correspondence since.
If you can't find it, HMRC's Inheritance Tax helpline (0300 123 1072) can trace it from the deceased's name and date of death.
02
Boxes 4–5 — your reference and phone number
Your own file reference (if you keep one) and a phone number HMRC can use if they have a query while processing the correction.
03
Box 6 — name and address of the firm or person dealing with the estate
The executor, administrator, or professional adviser HMRC should correspond with about this correction.
This doesn't have to be the same person who signs the declaration further down the form — but whoever signs must still be an accountable person in their own right (see Section 5).
The top of C4 establishes which estate and which original account you're amending. HMRC cross-checks these details against the IHT400 already on file, so they need to match exactly.
HM Revenue & Customs (HMRC) · C4❦
Section03
§33
Section 3
The four totals — how C4 works out the net change
This is the part of C4 that trips people up, because two of the four tables work in the OPPOSITE direction to what their heading suggests. Read this before filling in a single row.
01
Increases in value (box 7) — assets worth more, or missed off entirely
List any asset that has increased in value since the original IHT400, or any asset that wasn't included at all — for a missed asset, enter the previous value as 'NIL'.
Each row shows the previous value (column A), the amended value (column B), and the increase (column C = B minus A).
The total of column C goes in box 7.
02
Decreases in liabilities, exemptions or reliefs (box 8) — the one that confuses people
This table lists liabilities that have gone DOWN, or exemptions/reliefs that have gone down or are no longer due.
Because a smaller liability or a smaller exemption both mean a LARGER taxable estate, box 8's total is added to box 7 — not subtracted — to reach box 9, the total increase in the estate's value.
If nothing here has changed, box 8 is nil, and box 9 simply equals box 7.
03
Decreases in value (box 10) and increases in liabilities, exemptions or reliefs (box 11) — the mirror pair
These work the same way in reverse: assets worth less (box 10) plus liabilities, exemptions or reliefs that have gone UP or become newly due (box 11) both reduce the estate's value.
Box 10 plus box 11 gives box 12, the total decrease.
The same logic that makes box 8 count as an increase makes box 11 count as a decrease — a bigger liability or a bigger exemption both shrink the taxable estate.
04
Boxes 13–14 — the original figure and the corrected figure
Box 13 is the value HMRC already has on file — the form tells you exactly where to find it: box 108 on page 10 of IHT400, or the figure shown on the last calculation HMRC sent you.
Box 14 is the corrected estate value: box 13 plus box 9 (total increases) minus box 12 (total decreases).
This is the number the rest of the correction turns on.
This is the part of C4 that trips people up, because two of the four tables work in the OPPOSITE direction to what their heading suggests. Read this before filling in a single row.
HM Revenue & Customs (HMRC) · C4❦
Section04
§44
Section 4
Boxes 15–17: the tax figure — or let HMRC work it out
The last numbered boxes translate the corrected estate value into a tax figure. Most executors filing without professional help are better off leaving this part blank.
01
You don't have to do the tax calculation yourself
The form says so directly: if you're filling in C4 without a solicitor or other professional adviser and you want HMRC to calculate the tax due, leave boxes 15, 16 and 17 blank.
HMRC will work out the revised figure from box 14 and the account details already on file.
02
Box 15 — tax now due
If you (or your adviser) have calculated the revised tax figure yourselves, it goes here.
03
Box 16 — tax previously paid
The amount of Inheritance Tax the estate has already paid, as shown on the original IHT400 calculation.
04
Box 17 — tax payable or repayable as a result of the amendment
The difference between boxes 15 and 16 — a positive figure if more tax is due, a repayment if the correction reduces the bill.
Leave this blank along with boxes 15 and 16 if you want HMRC to do the arithmetic.
The last numbered boxes translate the corrected estate value into a tax figure. Most executors filing without professional help are better off leaving this part blank.
HM Revenue & Customs (HMRC) · C4❦
Section05
§55
Section 5
Reporting a change, repayment authority, and the signing rule
The last page of C4 covers three things: an explanation box HMRC specifically asks for, your bank details if a refund is coming, and a declaration with one of the strictest signing rules on any HMRC form.
01
Reporting a change — why the box exists
If you're reporting a change in value for stocks and shares, land or buildings, or removing an asset in its entirety, C4 asks you to explain why in a free-text box.
This is where a brief, factual explanation belongs — for example, 'a bank account omitted from the original account, found during final reconciliation' — not a lengthy narrative.
02
Repayment authority
If HMRC owes the estate a refund, they pay it by Faster Payments directly to a bank account, identified on the statement by the Inheritance Tax reference number.
Give the account name, sort code and account number here if a repayment is expected.
03
Every accountable person must sign — personally
This is the rule that catches people out most often: C4 must be signed by every person who delivered the original IHT400 account, and HMRC's guidance is explicit that a claim signed by an agent — a solicitor or accountant acting on the executors' behalf — cannot be accepted.
If three people signed the original IHT400, the same three sign C4, even if only one of them is doing the legwork.
The form provides space for up to four signatures (first through fourth representative); if more than four accountable persons need to sign, attach a separate sheet.
04
The declaration itself
Above the signatures, the form states plainly: if you give false information you may have to pay a financial penalty and face prosecution.
Each signatory is declaring, to the best of their knowledge and belief, that the information given is correct and complete — the same standard as the original IHT400 account.
The last page of C4 covers three things: an explanation box HMRC specifically asks for, your bank details if a refund is coming, and a declaration with one of the strictest signing rules on any HMRC form.
HM Revenue & Customs (HMRC) · C4❦
Section06
§66
Section 6
After you send form C4
What happens once the correction reaches HMRC, and what a late correction can cost.
01
HMRC recalculates the tax
Using the corrected figures, HMRC works out whether the estate has underpaid or overpaid.
An underpayment is demanded, typically with interest for the period the tax was outstanding.
An overpayment is refunded — by Faster Payments to the account given in the repayment authority section, or by cheque if no account was provided.
02
There's no published C4-specific turnaround time
HMRC doesn't publish a service-level target specific to C4, separate from the general IHT400 processing markers.
Don't quote a fixed number of weeks to a family expecting a refund — set expectations around 'HMRC will confirm once they've recalculated', not a specific date.
03
Late correction can mean more than interest
Beyond interest on any underpaid tax, a correction delivered more than six months after the defect was discovered risks a penalty — the Act's provisions for inaccurate and late-corrected accounts sit alongside the interest, not instead of it.
The safest position is simple: the moment you discover an error, the six-month clock is running — treat it as a real deadline, not a soft target.
What happens once the correction reaches HMRC, and what a late correction can cost.
HM Revenue & Customs (HMRC) · C4❦
Many people file C4 themselves — that is what this walkthrough is for. If the situation behind it has stopped being simple — beyond what a careful person can safely do alone — Signum, Valoren’s own specialist desk, can take it on, and we say so plainly: it starts with a free intake, and if you do not need us, we will tell you. Prefer an independent adviser? STEP and the Chartered Institute of Taxation both keep public member directories, and neither pays Valoren a referral fee.
FAQ
C4 questions, answered.
01What is form C4 used for?›
Form C4 tells HMRC that a previously delivered Inheritance Tax account — almost always IHT400 — was wrong, and gives the corrected figures.
It covers both directions: the estate having paid too much tax, or too little.
02When must I file form C4?›
Within six months of discovering the error, under section 217 of the Inheritance Tax Act 1984.
The six months runs from the date you discover the mistake — not from the date of death, and not from when IHT400 was originally filed.
03Is there a fee to file form C4?›
No. There is no fee to correct an Inheritance Tax account.
04Who has to sign form C4?›
Every accountable person who delivered the original IHT400 account, signing personally.
HMRC's guidance is explicit: a claim signed by an agent — a solicitor or accountant acting on the executors' behalf — cannot be accepted.
05I sold a house or shares for less than the value on the original account — do I use form C4?›
No. C4 cannot be used to claim a reduction resulting from a sale of land or shares.
Use IHT38 for land or buildings, or IHT35 for quoted shares and securities.
06I need to change a transferable nil-rate band claim — is that C4?›
No. C4 doesn't cover a change to the transferable nil-rate band available from an earlier death.
Write to HMRC directly explaining what's changed, or amend the original claim on form IHT402.
07What happens after I send form C4?›
HMRC recalculates the estate's Inheritance Tax using your corrected figures.
An underpayment is demanded, usually with interest; an overpayment is refunded to the bank details given in the repayment authority section.
HMRC doesn't publish a fixed turnaround time specific to C4.
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Where this fits
C4 is one form. The file behind it is the rest.
A correction is fastest when the original IHT400 figures are already on file, not being reconstructed from memory five years later.
Legal Instruments holds the account itself and the grant; the Property Folio and Financial Accounts records hold the asset detail behind whatever changed.
HM Revenue & Customs (HMRC)·17 fields·Free to file — no HMRC fee for a correction·30–40 minutes (with the original IHT400 figures already in the file) with Valoren
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