How Washington Calculates Child Support

Washington uses the Income Shares model to determine child support obligations. This page explains the guidelines, formula, and key factors.

Model Type

Income Shares (RCW 26.19)

Washington looks up a PER-CHILD amount from its economic table by combined monthly net income and number of children, multiplies it by the number of children, and splits the result by each parent's share of income. Unlike most states there is no parenting-time credit at all — the number of overnights does not change the guideline amount.

Sources & Verification

Core formula verified; some gaps disclosed below

Guideline effective 2026-01-01 · last checked against the primary source 2026-09-20

Primary sources

RCW 26.19.020 — Child support economic table (as replaced by 2025 c 272 § 14)RCW 26.19.071 — Standards for determination of income RCW 26.19.065 — Limitations and the self-support reserve WSCSS Economic Table (01/2026), Administrative Office of the Courts

What this calculator doesn't yet handle

The 479-row economic table was parsed from the Legislature's HTML rendering of RCW 26.19.020 and cross-checked cell-for-cell against the AOC's own 01/2026 PDF (2,395 of 2,395 cells identical) and against DCS's 01/2019 pamphlet over the 99 overlapping rows (495 of 495 identical). This is the strongest schedule provenance of any state on this site.
Washington's economic table gives a PER-CHILD amount that the worksheet multiplies by the number of children, unlike every other income-shares schedule here. Its age-bracket columns (0-11 / 12-18) were eliminated effective 2019-01-01; the Administrative Office of the Courts still serves two superseded PDFs showing them, which this calculator does not use.
Net income is entered directly rather than estimated from gross. RCW 26.19.071(5) is a closed list of amounts actually paid — mandatory pension contributions, union dues, and L&I industrial insurance premiums cannot be derived from gross income (L&I is an hourly, employer-risk-class figure), and Washington publishes no gross-to-net conversion table. The result is only as accurate as the net figures entered.
The self-support reserve ($2,394/month, 180% of the 2026 federal poverty guideline for one person) rose sharply on 2026-01-01 and must be refreshed each January when HHS republishes the guidelines. It is tracked in docs/guideline-watch/watchlist.json.
The income-share proportion is rounded to three decimal places, which is what every one of the AOC's published worked examples does and is required to reproduce their figures exactly. The instruction text itself only says 'divide,' so this is inferred from the examples rather than stated as a rule.
The AOC's own line-15 worked example is internally inconsistent: it adds the parent's line 7 rather than the limited line 9, silently dropping the self-support-reserve limitation it demonstrated one line earlier. This calculator implements the worksheet's stated formula (line 9 + line 14), not the example's arithmetic.
No parenting-time credit is computed, because Washington has none — no overnight threshold, no percentage-of-time formula, and no shared-parenting worksheet. A residential-schedule deviation under RCW 26.19.075(1)(d) is available but is discretionary, evidence-based, and requires written findings, so it is disclosed rather than estimated.
The 45% net-income limitation (RCW 26.19.065(1)) is surfaced as an informational figure, not applied as a cap. The official worksheet places it in 'Part VII: Additional Informational Calculations' and the standard calculation never references it; it also measures a parent's obligation across all of their children in every case, which a single-case calculator cannot know. Several third-party Washington calculators apply it as a hard cap — that is not what the worksheet does.
For an even (50/50) residential schedule, Washington fixes no rule for which parent makes the transfer payment; the worksheet computes both columns and leaves the direction to the parenting plan and the court. This calculator shows the larger figure and says the direction is undetermined.
The residential split adjustment (each parent the primary residential parent for a different child, per the AOC's optional RSA attachment) is not implemented, consistent with every other income-shares state here. Postsecondary educational support (RCW 26.19.090, advisory and not mandatory), the three-parent worksheet, imputed income (RCW 26.19.071(6)), and the RCW 26.19.075 deviation factors are disclosed rather than computed.