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

Section 1 -- Quick reference

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):

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

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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."

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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

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

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

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.

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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.

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

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

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.

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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)

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 = 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.

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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)

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

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.

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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.

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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.

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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

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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.

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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

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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.

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