Data Source and Methodology
Authoritative Data Source: Connecticut Department of Revenue Services (DRS) — Individual Income Tax, Rate Schedules and CT‑1040 Instructions (most recent). References:
- Connecticut DRS — Individuals: Resident Income Tax, Tax Information (accessed 2025-09-13). View official page
- Current Year Forms, Calculators and Tables. View official resources
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
\[ \text{Tax}(T) = \sum_{i=1}^{n} \max\!\big(0,\ \min(T, u_i) - l_i\big)\cdot r_i \] Marginal rate: \[ r_{\text{marginal}} = r_k \quad \text{such that } T \in [l_k, u_k) \] Effective rate: \[ r_{\text{effective}} = \begin{cases} \dfrac{\text{Tax}(T)}{T}, & T>0\\[6pt] 0, & T=0 \end{cases} \] Optional Personal Tax Credit c (0–0.75 as a fraction): \[ \text{Tax}_{\text{after}}(T) = \max\!\big(0,\ \text{Tax}(T)\cdot(1-c)\big) \]
Glossary of Variables
- Tax year: 2023 or 2024 Connecticut rate schedules.
- Filing status: Single, Married Filing Jointly (MFJ), Married Filing Separately (MFS), Head of Household (HOH).
- Connecticut taxable income T: Your taxable income for CT purposes (from CT‑1040).
- Gross wages: Annual salary or wages before taxes and pre‑tax deductions.
- Pre‑tax deductions: Amounts such as 401(k) and HSA that reduce wages before tax.
- Personal Tax Credit (%): State credit that reduces CT income tax based on CT AGI and filing status.
- Marginal rate: Percentage applied to your last dollar of taxable income.
- Effective rate: Total CT tax divided by taxable income.
- Per‑paycheck tax: Annual CT tax divided by the number of pay periods selected.
Worked Example
How It Works: A Step‑by‑Step Example
Suppose tax year 2024, filing status Single, and Connecticut taxable income T = $85,000. Connecticut’s 2024 rates (Single) are 2%, 4.5%, 5.5%, 6%, 6.5%, 6.9%, and 6.99% with thresholds at $10,000, $50,000, $100,000, $200,000, $250,000, and $500,000.
- First $10,000 at 2% → $200.
- Next $40,000 (10k–50k) at 4.5% → $1,800.
- Next $35,000 (50k–85k) at 5.5% → $1,925.
Total tax before any credits = $200 + $1,800 + $1,925 = $3,925.
Marginal rate = 5.5% (because $85k falls in the third bracket). Effective rate ≈ $3,925 / $85,000 ≈ 4.62%.
If you have a 10% Personal Tax Credit: Tax after credit = $3,925 × (1 − 0.10) = $3,532.50.
Frequently Asked Questions (FAQ)
Which taxes are included?
Only Connecticut state income tax. Federal taxes and payroll taxes (Social Security and Medicare) are excluded.
Do you include Connecticut exemptions and all credits automatically?
No. Exemptions and certain credits vary by situation. For transparency, this tool focuses on the official rate schedules and lets you optionally apply the Personal Tax Credit if you know your percentage.
What if I don’t know my CT taxable income?
Use the Estimate from Gross Pay mode. It estimates CT taxable income as gross wages minus pre‑tax deductions. This is an approximation; your actual CT taxable income may differ.
Why are my results different from my paycheck?
Employers use withholding tables and may account for allowances, adjustments, and timing differences. This calculator estimates annual liability rather than payroll withholding nuances.
Are the 2024 rates different from 2023?
Yes. Connecticut reduced the rates for the first two brackets in 2024. Always check the DRS instructions for the year you’re filing.
Is Head of Household supported?
Yes. This tool supports HOH. Some thresholds are aligned with Single for estimation; consult CT‑1040 instructions for precise details.
Can I use this for tax filing?
No. It is an educational tool. Use official forms and instructions or consult a qualified tax professional.