I picked the standard deduction but itemizing would've saved more — can I change it?
Article 17 of the Income Tax Act says the taxpayer deducts "either the standard deduction or the itemized deductions" (擇一減除). The National Taxation Bureaus apply it strictly:
The rule
Article 17 of the Income Tax Act says the taxpayer deducts "either the standard deduction or the itemized deductions" (擇一減除). The National Taxation Bureaus apply it strictly:
- If you selected the standard deduction on your return, or
- If your return listed no itemized deductions and didn't specify the standard deduction either (you're deemed to have chosen standard) —
then once the bureau has assessed (核定) your case, you cannot ask to switch to itemized deductions. This applies even if you later discover itemizing would have saved you money. The Kaohsiung National Taxation Bureau states the rule plainly in its filing-season guidance, and it has been applied to deny retroactive donation deductions where the taxpayer had already been assessed under the standard deduction.
Standard vs. itemized: the comparison to run first
For the 2025 tax year (filed May 2026):
| Single | Married filing jointly | |
|---|---|---|
| Standard deduction | NT$131,000 | NT$262,000 |
Itemizing means adding up the six categories — donations, insurance premiums, medical expenses, disaster losses, mortgage interest on an owner-occupied home (up to NT$300,000), and rent (for older tax years) — and supporting each with documentation. The Ministry of Finance's own advice is simple: compare the totals. If your itemizable amount exceeds the standard deduction, itemize; otherwise take the standard deduction and skip the paperwork.
How to avoid the trap
- Run the numbers before May. Add up donations, insurance, medical bills, and mortgage interest early — don't discover the better option in June.
- You can amend within the filing period. If you filed in early May and spot the mistake before the May 31 deadline, file a corrected return. After the deadline — and especially after assessment — the door closes.
- Watch the "deemed standard" trap. Leaving the deduction section blank doesn't preserve your options; it counts as choosing the standard deduction.
- Keep receipts anyway. Even if you take the standard deduction this year, next year's comparison needs this year's records.
Frequently asked questions
What if the tax office made an error — can I still correct it?
Correcting a genuine filing error (wrong number, missing income) is different from changing your deduction choice. Error corrections follow the normal reassessment rules; a voluntary switch from standard to itemized after assessment is what's barred.
Does this rule also block switching from itemized to standard?
The bureau guidance is written around the common case (standard → itemized), but the principle is symmetric: the choice, once assessed, stands. Run the comparison first and you won't need to test the other direction.
I donated to a temple that registered after I filed — can I claim it now?
Only if your case hasn't been assessed yet and you're still within the rules for amendment. If you were assessed under the standard deduction, the bureau has specifically said no — the donation can't be recognized retroactively in that situation.
Sources
- https://www.taipeicpb.org.tw/news/index.php?id=2334
- https://www.president.gov.tw/File/Doc/d8ff8892-7abb-4466-aabb-fd053cfedf78
- https://www.pac-cpas.com.tw/upfile/news/202505091441261530302.pdf