Imported from openaccountants/openaccountants (agent-skills/us-quarterly-estimated-tax/SKILL.md). Install upstream with npx skills add openaccountants/openaccountants --skill us-quarterly-estimated-tax. Copyright stays with the author (AGPL-3.0-or-later (code) / OpenAccountan).

US Quarterly Estimated Tax (Form 1040-ES) -- Self-Employed Skill v2.0

General reference only. This skill is general tax/accounting reference material for AI-assisted workflows. It has not been reviewed for any specific person's facts, documents, elections, deadlines, residency, filing status, or local procedures. Do not rely on it to file, pay, amend, or take a tax position without review by a qualified professional in the relevant jurisdiction.

Section 1 -- Quick reference

Quarterly due dates (TY2025):

Safe harbour thresholds:

Conservative defaults:

Section 2 -- Required inputs and refusal catalogue

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

3.2 Timing-based identification

3.3 Related but NOT federal estimated tax

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

Input: Single. TY2024 AGI = $95,000. TY2024 tax = $18,000. Expected TY2025 tax = $22,000. No withholding.

Example 2 -- High-income 110% rule

Input: MFJ. TY2024 AGI = $210,000. TY2024 tax = $42,000. Expected TY2025 tax = $55,000.

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

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 = 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 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

Each instalment = required annual payment / 4 (25% each).

5.5 Annualized income instalment method (Form 2210 Schedule AI)

Required instalment = 25% of annualized tax, minus prior payments. Must be elected for all four quarters.

5.6 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

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)

The "penalty" is interest on the underpayment. Rate = federal short-term rate + 3 percentage points, compounded daily.

6.2 Published rates (TY2025)

(Verify against IRS Revenue Rulings.)

6.3 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

IRS may waive under IRC 6654(e)(3) for: casualty/disaster/unusual circumstances, retirement after age 62, or disability.

Section 7 -- Special situations

7.1 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

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

Annualized method (Section 5.5) adjusts for uneven income. Alternatively, adjust future estimates up or down.

7.4 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

EC1 -- Prior year short tax year. Prior year < 12 months: prior-year safe harbour unavailable. Only 90% current year.

EC2 -- Prior year zero tax but high AGI. Zero tax = $0 required annual payment under Method B. The zero-tax rule dominates.

EC3 -- Taxpayer dies mid-year. Estimated payments required only through quarter of death.

EC4 -- Large Q4 income. Prior-year safe harbour typically best. Annualized method shows low Q1-Q3 and large Q4.

EC5 -- W-2 to self-employment mid-year. W-2 withholding treated as ratable. Annualized method reduces Q1/Q2 required amounts.

EC6 -- Overpayment. Applied to next year or refunded (Form 1040 line 36).

EC7 -- Unequal payments. Penalties computed per-quarter. Q1 shortfall not cured by Q2 overpayment.

EC8 -- Disaster area relief. IRS may postpone due dates. Verify announcements.

EC9 -- Farmer/fisherman. Single January 15 payment or file by March 1.

EC10 -- NIIT creates unexpected requirement. 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. Log in to access the latest version, request a professional review from a licensed accountant, and track updates as tax law changes.

Source: OpenAccountants — open tax Guides for AI, reviewed by named CPAs/CAs/EAs. Quality: source-cited draft. For always-current figures and named-accountant backing, connect the OpenAccountants MCP server (openaccountants-mcp).