The Illinois 13.3.1, line by line

The Illinois Supreme Court form 13.3.1 is the financial affidavit every parent has to file in almost every Illinois case that touches money — divorce, parentage, child support, maintenance. It is fourteen pages. It has roughly seventy fillable fields across four sections. Most of those fields are obvious. About a dozen of them are not, and those are the ones that get parents in trouble.

This page walks every section in order. For each section, you will get plain English on what the form is asking, which documents to pull, the statutory references that drive the answer, and the most common mistake.

Header and case caption

Top of page 1. The case caption identifies the court, the case number, and the parties.

• Court: the circuit court of the county where the case was filed. Lake County is "In the Circuit Court of the Nineteenth Judicial Circuit, Lake County, Illinois." Cook is "In the Circuit Court of Cook County, Illinois." Match exactly what your existing pleadings say.
• Case number: the docket number assigned at filing. It is on every notice you have received from the court.
• Petitioner / Respondent: the spouse who filed the case is petitioner. The other spouse is respondent. Do not swap these even if you are responding to a counter-petition — the original filer is always petitioner on the case caption.

Common mistake: filling in your own name as petitioner because you are the one filling out the affidavit. The case caption is the case caption. It does not change based on who is filling out which document.

Section I — Personal info (lines 1-4)

Line 1: Your name, address, and date of birth

The address you list is your current residential address as of the date you sign the form. If you have moved during the case, the address on this form should be your current one, not the one on the original petition.

Line 2: Employer and employment status

Name of your current employer, your job title, and the date you started. If you are self-employed, write "Self-employed" and the legal name of your business. If you are between jobs, write "Unemployed" with the date of last employment.

Line 3: Number of dependents

Count every minor child you have a legal duty to support, plus any other dependents who actually depend on your income. Children from a previous relationship who you currently support count here.

Line 4: Health insurance and the children

Whether you currently carry health insurance for your minor children, and the monthly cost attributable to them. This number ties to line 4 of the Illinois child-support worksheet later in your case, so it matters.

Section II — Income (lines 5-9)

Section II is the part of the form where most DIY filers go wrong. Slow down here.

Line 5: Gross monthly income

Your gross monthly income from all sources before any deductions. The form wants you to list each source separately (W-2 wages, self-employment income, rental income, dividend income, etc.) and total them.

For W-2 income, multiply your annual gross from your most recent W-2 by 1/12 — or if your income varies, take a 12-month rolling average. For an hourly worker, multiply hours per pay period by hourly rate by number of pay periods per year, then divide by 12.

For self-employment, use net Schedule C income (revenue minus business expenses) divided by 12. The Illinois child-support guidelines explicitly use net Schedule C for self-employment and that is what the 13.3.1 follows.

Line 6: Deductions allowed by statute

Itemize the statutory deductions you take from line 5 before you arrive at line 7. The deductions allowed under 750 ILCS 5/505(a)(3.1) are:

• Federal income tax (properly calculated as if you were single or HoH for the period in question).
• State income tax (properly calculated).
• Social Security tax (FICA, currently 6.2% up to the wage base).
• Medicare tax (1.45%).
• Mandatory union dues.
• Mandatory retirement contributions required as a condition of employment (most are not — see below).
• Dependent health insurance premiums.
• Life insurance premiums for the obligor where the policy is required by court order.
• Prior-order child support actually paid.
• Spousal maintenance actually paid pursuant to a prior order.

Voluntary 401(k) contributions, voluntary additional life insurance, and voluntary deductions in general are not allowed. This is the line where parents accidentally deflate their reported net income by listing voluntary 401(k) as a deduction. Do not do it.

Line 7: Net monthly income

This is the most important line on the form. Line 7 is line 5 minus the statutory deductions you listed on line 6. It is the figure the court uses to calculate income share child support. It is the figure that drives maintenance calculations under 750 ILCS 5/504.

Line 7 is almost never the same as your actual take-home pay. Take-home reflects every deduction your employer pulls — including voluntary ones the statute disregards. Statutory net is, by design, higher than take-home for most parents.

If you cannot reconcile your line 7 against your bank deposits, that is normal. The court does not expect statutory net to match observed deposits. It expects the math from line 5 minus line 6 to be correct.

Line 8: Other income

Income from sources outside line 5: bonuses, commissions paid irregularly, distributions from a closely held business, gift income, trust distributions, gambling winnings, etc. List the source and the monthly equivalent. If a bonus is paid annually, divide by 12.

Line 9: Year-to-date totals

Total gross income year-to-date as of the date you sign the affidavit. Pull this from your most recent pay stub (most pay stubs list YTD gross). Combine sources if you have more than one income stream.

Section III — Expenses (lines 10-15)

Line 10: Housing

Monthly rent or mortgage payment, plus monthly property tax escrow if applicable, plus monthly homeowner's insurance escrow if applicable, plus HOA dues. If you escrow property tax and insurance with your mortgage, your total monthly housing cost is the full mortgage payment (PITI). If you do not escrow, add them separately.

Line 11: Utilities

Twelve-month average of electric, gas, water, sewer, trash, internet, mobile phone, and any recurring utility. Use a twelve-month average rather than a single month because utilities fluctuate seasonally and Illinois winters skew gas bills heavily.

Line 12: Transportation

Auto loan payments, auto insurance, fuel, maintenance, parking, public transit. The form breaks these into separate sub-lines on the 2017+ version. Public transit users in Chicago should include CTA/Metra passes here.

Line 13: Children and household

Childcare, school costs not covered by tuition, extracurricular activities, clothing, groceries (allocate as best you can — there is no perfect way), out-of-pocket healthcare for the children. If you pay childcare in cash, write it down anyway. The form expects all recurring expenses, not just the ones with paper trails.

Line 14: Monthly debt service

The total of every minimum monthly payment you make on every debt you owe. Payment, not balance. Credit cards, personal loans, student loans (federal and private), auto loans separate from the auto cost on line 12 if the form wants them separately, medical debt payment plans.

Leaving line 14 blank or wrong is the second most common mistake on a DIY 13.3.1, after the line 5/7 confusion. Pull every recent statement, find the "minimum payment due" or "monthly amount," and total them.

Line 15: Other recurring expenses

Anything else over a normal threshold that recurs monthly: subscriptions, professional membership dues, gym, recurring charitable giving, alimony you pay from a previous marriage, etc. The court is not interested in your $9 Spotify charge but is very interested in your $400-a-month country-club membership.

Section IV — Assets and debts

Asset schedule

Every asset in your name (sole or joint), with its current value and the source of that valuation. Categories:

• Real estate at fair market value, with the basis for the valuation (recent appraisal, Zillow estimate, county assessment, etc.).
• Vehicles at fair market value, with Kelley Blue Book or NADA used as the standard.
• Bank accounts — every checking and savings account at the most recent statement balance.
• Retirement accounts — 401(k), IRA, pension, deferred comp.
• Investment accounts — brokerage, taxable mutual funds, HSAs over a threshold.
• Business interests — ownership stake and book value or recent valuation.
• Other — collectibles, jewelry, valuable personal property above a normal household threshold.

Debt schedule

Every debt in your name (sole or joint), with the current balance and the monthly payment. This is where credit-card balances and student-loan principal sit. The monthly payment column ties back to line 14 above.

Classification: marital vs non-marital

For each asset and debt, the form asks you to classify it as marital, non-marital, or disputed. Marital is anything acquired during the marriage with marital effort or marital funds. Non-marital is property owned before the marriage, plus gifts and inheritances received during the marriage.

Classification on the 13.3.1 is not binding on the court — the court makes the ultimate decision — but your classification has to match the rest of your case theory. If you are going to argue at trial that an asset is non-marital, you need to have classified it non-marital on the affidavit.

Attestation and signature

The last page of the 13.3.1 is the verification — the part where you swear, under penalty of perjury, that everything above is true and complete to the best of your knowledge. You sign and date.

As of 2024, the form no longer requires notarization in most Illinois counties (the verification under 735 ILCS 5/1-109 substitutes for a notarized affidavit). Check the local rule of your circuit before filing. A handful of judges still want notarized signatures.

Required exhibits

The 13.3.1 is not just the form itself. Most counties require supporting exhibits attached:

• Last two years of federal tax returns.
• Three to six months of pay stubs.
• Three to six months of bank statements for every account.
• Most recent retirement account statement.
• Current lease or mortgage statement.

Local rules vary. Cook County has its own General Order 86 setting out exact exhibit requirements. DuPage, Lake, and Kane each have their own local rules. Check the local rule before you file or you will be sent away to refile with the missing exhibits.

Where Casefile fits

Casefile reads each of those exhibits and populates the corresponding lines of the form. Three months of bank statements drop in, the system extracts every transaction, and your expense lines on Section III are populated with twelve-month averages already calculated. Your pay stubs feed line 5, line 6, and line 7 with the gross/deductions/net split done correctly the first time.

You still review every number. You still sign. But you do not have to assemble fourteen pages of data by hand from a pile of paper.

For a higher-level walkthrough of doing it manually, see the DIY Illinois affidavit guide. For the founder story, see the founder page.