--- oa_review_kit: v1 guide_slug: us-quarterly-estimated-tax guide_version: us-quarterly-estimated-tax@2026-05-23T15:25:07.087Z archetype: personal_income --- # Review kit: US Quarterly Estimated Tax Thank you for reviewing this Guide. This kit is one file with three parts: how to use it, an interview prompt for your AI, and the Guide itself. ## How to use this kit (3 steps, about 15 minutes) 1. Open the AI you already use (ChatGPT, Claude, Gemini, anything that reads markdown) and paste in everything from "INTERVIEW PROMPT" below, including the Guide at the end. 2. Your AI interviews you like a colleague, one question at a time. Just talk: war stories, walk-throughs, the mistakes you catch. No writing required. 3. Your AI writes your answers up as a single markdown file. Hand it back at openaccountants.com/skills/us-quarterly-estimated-tax/handback (also linked from the Guide page: "Hand back your file"). What you added is published under your name and credential. If your AI cannot produce the exact output format, hand back whatever you have: a revised Guide file, a worksheet, or plain notes. We take those too, and a person reviews them by hand. The format below is the one we can apply straight away. --- # INTERVIEW PROMPT (paste from here down into your AI) You are interviewing a practising accountant about how they actually do the work covered by the attached Guide ("US Quarterly Estimated Tax", slug `us-quarterly-estimated-tax`). Interview them like a colleague doing a handover. Do not lecture. Ask ONE question at a time and wait for the answer. Chase war stories and specifics: what kind of client, which portal step, how big the penalty was. The rates, thresholds, and citations are our job; we refresh those from primary sources. Capture ONLY what is NOT derivable from law: - order of operations, and what a wrong order corrupts - what to ask a client before computing anything - what to assume when a fact is unknown, and how it gets flagged - the most-missed traps, with penalty size and who falls in - how the portal or filing channel actually behaves - what has to reconcile before anyone signs - when to refuse the work and hand it to a human specialist If the accountant corrects a rate, threshold, or deadline in the Guide along the way, record it in the FACT CORRECTIONS table, but do not steer the interview toward numbers. ## Questions to work through Ask these in order, one at a time. Skip any the accountant has already covered; follow up where a story has specifics worth pinning down. Each question is tagged with the method slot(s) it feeds. 1. [intake_questions] A new personal-tax client sits down. What are your first five questions before you touch a number? 2. [intake_questions] [conservative_default] Which of those answers, if missing, makes you stop rather than estimate? 3. [evidence] Which documents do you insist on seeing, and which do you take the client's word for? 4. [sequence] In what order do you build the return, and what goes wrong when someone does it backwards? 5. [trap] What deduction or relief do clients most often believe they're entitled to but aren't? 6. [trap] What computation does software or AI most often get wrong on returns you've reviewed? 7. [judgment_rule] When the law gives two routes (regime choice, standard vs itemized, allowance vs actuals), how do you actually pick, and what do you write down about the choice? 8. [cross_check] What triggers the tax authority's mismatch letters in your experience, and what do you reconcile up front to prevent them? 9. [edge_case] Tell me about a client whose side income (platform, rental, foreign) changed the whole shape of the return. What did you do differently? 10. [filing_mechanics] Walk me through the e-filing itself: the verification step, the deadline nobody knows, what happens if the client doesn't do their part. 11. [scope_gate] What kind of personal-tax client do you turn away or send to a specialist? 12. [handback_protocol] What exactly do you hand the client before anything is filed? What's in your working paper? ## Method slots (for tagging the write-up) - `scope_gate` (Scope gate and refusals): when to stop and send the client to a human - `sequence` (Order of operations): what order to do things in, and what a wrong order corrupts - `intake_questions` (Client intake questions): what to ask a client before computing - `evidence` (Documents and evidence): which documents to insist on, and what is draft-grade vs file-grade - `judgment_rule` (Judgment rules): how a practitioner actually picks when the law allows two routes - `conservative_default` (Conservative defaults): what to assume when a fact is unknowable at draft time - `trap` (Traps and most-missed items): the mistakes everyone makes, what they cost, and who falls in - `filing_mechanics` (Portal and filing mechanics): how submission actually works: channel, order, what locks - `cross_check` (Cross-checks before signing): what has to reconcile with what before delivery, and how close is close enough - `pattern_library` (Pattern library): how messy real-world data (bank lines, payout platforms) maps to tax categories - `edge_case` (Edge-case playbook): the client situations that change the method, not just the numbers - `unsettled_law` (Unsettled-law flags): what not to finalise right now, and why - `handback_protocol` (Hand-back protocol): what the finished working paper contains and who reviews it ## Output format: oa-handback v1 When the interview is done, write the answers up as ONE markdown file in exactly this shape. Fill in the reviewer's real name, credential, and email (ask for them at the end if they have not come up). Every method block gets a `### [method:]` heading where `` is one of the 13 slot ids above. Keep `guide_slug` and `guide_version` exactly as given. Omit any section the interview produced nothing for, but keep the headings that remain exactly as shown. The `fact_key` column may be left blank when unknown. ```markdown --- oa_handback: v1 guide_slug: us-quarterly-estimated-tax guide_version: us-quarterly-estimated-tax@2026-05-23T15:25:07.087Z reviewer_name: reviewer_credential: # free text: CPA, EA, ACCA, Steuerberater... reviewer_email: verdict: --- ## METHOD ### [method:filing_mechanics] ### [method:intake_questions] - - ... ## FACT CORRECTIONS | fact_key | current | correct | source | |---|---|---|---| | | | | | ## FLAGS - [unsettled] - [refer] ## NOTES ``` If for any reason you cannot produce this exact format, output the accountant's corrections and methods as clear plain notes instead. The hand-back page accepts plain notes and revised Guide files too; this format is an optimization, never a gate. --- # THE GUIDE UNDER REVIEW --- name: us-quarterly-estimated-tax description: Use this skill whenever asked about US federal quarterly estimated income tax payments for sole proprietors and single-member LLCs. Trigger on phrases like "1040-ES", "estimated tax", "quarterly tax", "safe harbor", "underpayment penalty", "Form 2210", "annualized income", or any question about federal estimated tax requirements. Covers the $1,000 threshold, 100%/110% prior-year safe harbor, 90% current-year method, quarterly due dates, annualized income instalment method, Form 2210 penalty computation, and withholding strategies. MUST be loaded alongside us-tax-workflow-base v0.1+. Federal only. jurisdiction: US-FED domain: income-tax tax_year: 2025 --- # us-quarterly-estimated-tax ## US Quarterly Estimated Tax (Form 1040-ES) -- Self-Employed Skill v2.0 ## Verified rates & thresholds (accountant-reviewed) Reviewed against the cited tax authorities by **a licensed accountant** on 2026-06-03. Items flagged for further clarification are tracked separately and excluded here. This block is generated from verified `skill_facts` — edit the facts, not the prose. ### Estimated Tax (1040-ES) - **Threshold** — Owe >= $1,000 after withholding/credits _(IRC 6654; Form 1040-ES.)_ - **≤$150K** — Prior-year AGI <= $150,000 -> 100% prior-year safe harbor _(IRC 6654(d).)_ - **>$150K** — Prior-year AGI > $150,000 -> 110% prior-year safe harbor _(IRC 6654(d)(1)(C).)_ - **Current** — 90% of current-year tax _(IRC 6654(d).)_ - **Rate** — Federal underpayment rate was 7% for all four quarters of 2025 (set quarterly = federal short-term + 3 points) _(IRC 6621; IRS Pub 505; quarterly rev. rulings.)_ ## Section 1 -- Quick reference **Quick reference fields** | Field | Value | | --- | --- | | Country | United States (federal) | | Tax | Quarterly estimated income tax payments | | Forms | 1040-ES (vouchers), 2210 (underpayment penalty), 2210 Schedule AI (annualized) | | Primary legislation | IRC Section 6654 | | Supporting legislation | IRC Sections 6621, 6622, 1401, 1402, 3402 | | Authority | Internal Revenue Service (IRS) | | Portal | IRS Direct Pay (irs.gov/payments) / EFTPS | | Currency | USD only | | Threshold | Net tax due >= $1,000 after withholding and credits | | Safe harbours | 90% current year OR 100%/110% prior year | | Payment schedule | Apr 15, Jun 16*, Sep 15, Jan 15 (*Jun 15 is Sunday in 2025) | | Entity types | Sole proprietors, single-member LLCs (disregarded) | | Companion skill | us-tax-workflow-base v0.1+ | | Contributor | Open Accountants Community | | Validated by | April 2026 | | Validation date | April 2026 | **Quarterly due dates (TY2025 & TY2026)** | Instalment | Due date | Period | | --- | --- | --- | | 1st | April 15, 2025 | Jan 1 -- Mar 31 | | 2nd | June 16, 2025 | Apr 1 -- May 31 | | 3rd | September 15, 2025 | Jun 1 -- Aug 31 | | 4th | January 15, 2026 | Sep 1 -- Dec 31 | **Safe harbour thresholds** | Prior year AGI | Safe harbour percentage | | --- | --- | | AGI <= $150,000 ($75,000 MFS) | 100% of prior year tax | | AGI > $150,000 ($75,000 MFS) | 110% of prior year tax | **Conservative defaults** | Ambiguity | Default | | --- | --- | | Prior year AGI unknown | Assume > $150K; use 110% | | Underpayment rate uncertain | Use most recently published rate | | W-2 withholding + SE income | Compute explicitly; do not assume W-2 covers SE | | Annualized method considered | Default to equal instalments; flag for reviewer | | Mid-year income uncertain | Annualize YTD + 10% buffer | | Prior year return not filed | Use last filed return; flag | ### Required inputs - **Minimum viable** — expected total federal tax (income tax + SE tax + NIIT + Additional Medicare Tax), prior year total tax and AGI, expected withholding from all sources. - **Recommended** — prior year 1040 or transcript, current year Schedule C net profit estimate, W-2 withholding from spouse if MFJ. - **Ideal** — complete prior year return, current year quarterly P&L, upstream skill outputs (Schedule C, SE tax, QBI). - **Refusal policy if minimum is missing** — SOFT WARN. Without prior year data, safe harbour cannot be computed. ### Refusal catalogue - **R-US-ET-1 -- Corporate estimated tax (1120-W)** — Trigger: corporation. Message: "Corporate estimated tax is outside this skill." - **R-US-ET-2 -- Trust/estate estimated tax (1041-ES)** — Trigger: trust or estate. Message: "Trust/estate estimated tax is outside this skill." - **R-US-ET-3 -- State estimated tax** — Trigger: client asks about state payments. Message: "State estimated tax rules differ materially. Use the state-specific skill." - **R-US-ET-4 -- Nonresident alien (1040-ES NR)** — Trigger: nonresident alien. Message: "Nonresident alien estimated tax is outside this skill." ## Section 3 -- Payment pattern library This is the deterministic pre-classifier for bank statement transactions. When a debit matches a pattern below, classify it as a federal estimated tax payment. ### 3.1 IRS estimated tax debits **IRS estimated tax debits pattern table** | Pattern | Treatment | Notes | | --- | --- | --- | | IRS, INTERNAL REVENUE SERVICE | Federal estimated payment | Match with Apr/Jun/Sep/Jan timing | | EFTPS, ELECTRONIC FED TAX | Federal estimated payment | EFTPS payment | | IRS DIRECT PAY | Federal estimated payment | IRS online payment | | 1040-ES, 1040ES | Federal estimated payment | Explicit form reference | | ESTIMATED TAX PAYMENT, EST TAX | Federal estimated payment | Explicit description | | US TREASURY, TREASURY 310 | Federal estimated payment | Government payee | ### 3.2 Timing-based identification **Timing-based identification table** | Debit date range | Likely instalment | Confidence | | --- | --- | --- | | 10 April -- 20 April | 1st instalment (Apr 15) | High if IRS payee | | 10 June -- 20 June | 2nd instalment (Jun 15/16) | High | | 10 September -- 20 September | 3rd instalment (Sep 15) | High | | 10 January -- 20 January | 4th instalment (Jan 15) | High | ### 3.3 Related but NOT federal estimated tax **Related but not federal estimated tax table** | Pattern | Treatment | Notes | | --- | --- | --- | | STATE TAX, NYS, CA FTB, IL DOR | EXCLUDE | State estimated tax | | FICA, SOCIAL SECURITY | EXCLUDE | Employment tax (if separate) | | IRS PENALTY, IRS INTEREST | EXCLUDE | Penalty/interest | | IRS REFUND, TAX REFUND | Flag for reviewer | Refund | | 1040 BALANCE, TAX DUE | Flag for reviewer | Annual return balance payment | ### 3.4 Withholding vs estimated payments W-2 withholding appears as employer deductions on pay stubs, not as separate bank debits. Do not confuse employer withholding with estimated tax payments. ## Section 4 -- Worked examples ### Example 1 -- Basic prior-year safe harbour Single. TY2024 AGI = $95,000. TY2024 tax = $18,000. Expected TY2025 tax = $22,000. No withholding. **Method / Amount** | Method | Amount | | --- | --- | | Prior year (100%) | $18,000 | | Current year (90%) | $19,800 | | Required (lesser) | $18,000 | | Quarterly | $4,500 | ### Example 2 -- High-income 110% rule MFJ. TY2024 AGI = $210,000. TY2024 tax = $42,000. Expected TY2025 tax = $55,000. **Method / Amount** | Method | Amount | | --- | --- | | Prior year (110%) | $46,200 | | Current year (90%) | $49,500 | | Required (lesser) | $46,200 | | Quarterly | $11,550 | ### Example 3 -- Withholding eliminates requirement **Input:** MFJ. Spouse W-2 withholding = $25,000. TY2024 tax = $20,000. AGI = $120,000. **Output:** Withholding ($25,000) > 100% prior year ($20,000). No estimated payments required. ### Example 4 -- Under $1,000 threshold **Input:** Expected TY2025 tax = $5,200. Part-time W-2 withholding = $4,500. Net = $700. **Output:** Net tax due $700 < $1,000. No estimated payments required. ### Example 5 -- Bank statement classification **Input line:** `04/15/2025 ; IRS DIRECT PAY EST TAX ; DEBIT ; -4,500.00 ; USD` **Classification:** Federal estimated tax payment, 1st instalment TY2025. Tax payment -- not deductible on Schedule C. ## Section 5 -- Computation rules ### 5.1 The $1,000 threshold test - **$1,000 threshold test** — expected_tax = income_tax + SE_tax + Additional_Medicare + NIIT net_tax_due = expected_tax - withholding - refundable_credits if net_tax_due < 1,000: no estimated payments required ### 5.2 Required annual payment - **Required annual payment** — Required = lesser of: Method A (current year): 90% of TY2025 tax; Method B (prior year): 100% of TY2024 tax (110% if AGI > $150K / $75K MFS) ### 5.3 Prior year safe harbour requirements - **Prior year safe harbour requirements** — Prior year must be 12-month tax year. Prior year return must be filed. If prior year tax was zero: required annual payment under Method B = $0 ### 5.4 Quarterly instalments - **Quarterly instalments** — Each instalment = required annual payment / 4 (25% each). ### 5.5 Annualized income instalment method (Form 2210 Schedule AI) **Annualization factor table** | Period | Months | Annualization factor | | --- | --- | --- | | Period 1 | Jan-Mar | 4 | | Period 2 | Jan-May | 2.4 | | Period 3 | Jan-Aug | 1.5 | | Period 4 | Jan-Dec | 1 | - **Required instalment computation** — Required instalment = 25% of annualized tax, minus prior payments. Must be elected for all four quarters. ### 5.6 Withholding strategy (MFJ) - **Withholding strategy (MFJ)** — Increase W-2 spouse's withholding via Form W-4 Step 4(c). Withholding is treated as paid ratably throughout the year even if changed mid-year. ### 5.7 January 31 filing exception - **January 31 filing exception** — If return filed and all tax paid by January 31, 2026: 4th instalment not required. ## Section 6 -- Penalties and interest ### 6.1 Underpayment penalty (Form 2210) - **Underpayment penalty** — The "penalty" is interest on the underpayment. Rate = federal short-term rate + 3 percentage points, compounded daily. ### 6.2 Published rates (TY2025) **Published rates table** | Quarter | Rate | | --- | --- | | Q1 2025 | 7% | | Q2 2025 | 7% | | Q3 2025 | 7% | | Q4 2025 | 7% | | Q1 2026 | 7% | (Verify against IRS Revenue Rulings.) ### 6.3 Per-quarter computation - **Per-quarter computation** — for each quarter: required = 25% of required annual payment paid = estimated payments + allocable withholding underpayment = max(0, required - paid) period = instalment_due_date to earlier(payment_date, Apr 15 next year) penalty = underpayment x daily_rate x days_in_period ### 6.4 Waiver provisions - **Waiver provisions** — IRS may waive under IRC 6654(e)(3) for: casualty/disaster/unusual circumstances, retirement after age 62, or disability. _(IRC 6654(e)(3))_ ## Section 7 -- Special situations ### 7.1 Withholding strategy for married couples - **Withholding strategy for married couples** — Self-employed spouse + W-2 spouse: increase W-4 extra withholding to cover both. Withholding treated as ratable even if changed mid-year -- advantage over quarterly estimates. ### 7.2 First year of self-employment - **First year of self-employment** — If prior year tax was zero: required annual payment under prior-year method = $0. No estimated payments required under that method. ### 7.3 Mid-year income changes - **Mid-year income changes** — Annualized method (Section 5.5) adjusts for uneven income. Alternatively, adjust future estimates up or down. ### 7.4 Farmer/fisherman exception - **Farmer/fisherman exception** — 2/3 of income from farming/fishing: single instalment by January 15, or file by March 1 and pay in full. ## Section 8 -- Edge cases Prior year < 12 months: prior-year safe harbour unavailable. Only 90% current year. Zero tax = $0 required annual payment under Method B. The zero-tax rule dominates. Estimated payments required only through quarter of death. Prior-year safe harbour typically best. Annualized method shows low Q1-Q3 and large Q4. W-2 withholding treated as ratable. Annualized method reduces Q1/Q2 required amounts. Applied to next year or refunded (Form 1040 line 36). Penalties computed per-quarter. Q1 shortfall not cured by Q2 overpayment. IRS may postpone due dates. Verify announcements. Single January 15 payment or file by March 1. Investment income above NIIT threshold ($200K single / $250K MFJ) adds 3.8% to total tax. ## Section 9 -- Self-checks Before delivering output, verify: - [ ] $1,000 threshold test applied - [ ] Both safe harbour methods computed (prior year and current year) - [ ] Correct prior-year percentage used (100% vs 110% based on AGI) - [ ] All four quarterly due dates correct - [ ] Withholding from all sources included - [ ] SE tax + income tax + NIIT + Additional Medicare included in total tax - [ ] Annualized method flagged if income is uneven - [ ] First-year zero-prior-tax rule checked - [ ] State estimated tax deferred to state skill - [ ] Output labelled as estimated until reviewer confirms ## Section 10 -- Test suite ### Test 1 -- Basic prior-year safe harbour **Input:** Single. TY2024 AGI $95K, tax $18K. TY2025 expected $22K. No withholding. **Expected:** Required = $18,000 (100% prior). Quarterly = $4,500. ### Test 2 -- High-income 110% **Input:** MFJ. TY2024 AGI $210K, tax $42K. TY2025 expected $55K. **Expected:** Required = $46,200 (110% prior). Quarterly = $11,550. ### Test 3 -- Withholding covers safe harbour **Input:** MFJ. Spouse withholding $25K. TY2024 tax $20K. AGI $120K. **Expected:** No estimated payments required. ### Test 4 -- Below $1,000 **Input:** Expected tax $5,200. W-2 withholding $4,500. **Expected:** Net $700 < $1,000. No payments required. ### Test 5 -- Underpayment penalty **Input:** Required $5,000/quarter. Q1 paid $3,000. Q2-Q4 paid $5,000. Rate 7%. **Expected:** Q1 underpayment $2,000. Penalty approx. $140 (full year). ### Test 6 -- First year, zero prior tax **Input:** First year. No prior return. **Expected:** Prior year method = $0. No payments required under that method. ### Test 7 -- Farmer exception **Input:** 2/3+ farming income. Expected tax $25,000. **Expected:** Single payment Jan 15 or file by Mar 1. ## Prohibitions - NEVER file estimated payments or generate payment instructions -- compute amounts only - NEVER recommend intentional underpayment as a strategy - NEVER compute state estimated tax -- defer to state skills - NEVER override reviewer's method selection - NEVER guarantee a safe harbour eliminates all penalties mid-year - NEVER advise on entities other than sole proprietors / disregarded SMLLCs - NEVER apply penalty waiver without reviewer approval - NEVER present amounts as definitive -- label as estimated ## Disclaimer This skill and its outputs are provided for informational and computational purposes only and do not constitute tax, legal, or financial advice. Open Accountants and its contributors accept no liability for any errors, omissions, or outcomes arising from the use of this skill. All outputs must be reviewed and signed off by a qualified professional (such as a CPA, EA, tax attorney, or equivalent licensed practitioner in your jurisdiction) before filing or acting upon. The most up-to-date, verified version of this skill is maintained at [openaccountants.com](https://openaccountants.com). Log in to access the latest version, request a professional review from a licensed accountant, and track updates as tax law changes. ## Talk to a verified accountant This skill is a tool, not an engagement. Every taxpayer's situation is different, and the rules in the skill may not match your specific facts. To speak with one of the licensed accountants who verifies skills for your jurisdiction — **no liability on either side until you and the accountant sign a formal engagement letter** — book a free 30-minute call: **→ [Book a call](https://calendly.com/openaccountants-info/30min)** We'll route you to the named verifier covering your country or state. 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