How this calculator works
Tennessee child support is calculated by following a specific sequence of steps set out in Rule 1240-02-04. The calculator implements those steps exactly. This page walks through them in plain English.
The big picture
Tennessee uses the Income Shares Model. The idea: children should receive the same proportion of parental income that they would have received if the parents lived together. The calculator works in three phases:
- Establish the baseline — combine the parents' income, find the Basic Child Support Obligation (BCSO).
- Allocate between parents — split the BCSO by each parent's percentage of combined income.
- Adjust for circumstances — parenting time, add-ons, deviations.
The Box 5 trap
If you're using a W-2, you must use Box 5 (Medicare wages), not Box 1. Box 1 is net of voluntary 401(k) / 403(b) contributions — the Guidelines don't permit deducting those. For high earners, the difference can change the final obligation by hundreds of dollars per month.
The three income zones
- SSR zone (very low income obligor): A Self-Support Reserve check applies — the lower of pro-rata BCSO or obligor-only BCSO is used.
- Schedule zone (combined AGI ~$1,200 to $28,250): Direct lookup from the BCSO Schedule, rounded UP to the next $50.
- Above-cap zone (over $28,250): Top-of-schedule plus a percentage of the excess (6.81% / 7.22% / 7.77% / 8.05% / 8.66% by number of children). The 4-child rate is 8.05%, not the 8.25% some third-party sources state.
50/50 parenting
For equal parenting (182.5 days each), the rule designates one parent as the ARP solely for purposes of the adjustment, and the variable multiplier becomes exactly 2.0. The algebra reduces to:
Net support = BCSO × |PI_A − PI_B| Direction: higher-earning parent → lower-earning parent
Per Rule .04(7)(f), when the PRP-by-designation actually earns more than the ARP-by-designation, support flows from PRP to ARP.
Add-ons vs. deviations
Add-ons (health insurance premium for the children, recurring uninsured medical, work-related childcare) are mandatory and allocated pro-rata to income share.
Private school is a discretionary deviation — not a mandatory add-on. The court must make written findings that the deviation is in the child's best interest and consistent with the parents' finances. If granted, it is allocated pro-rata.
Special expenses (camp, lessons, travel, school clubs) have a unique 7% threshold: only amounts exceeding 7% of monthly BCSO are considered as a deviation, unless the parties agree to waive the threshold.
Lifecycle
This calculator produces a single-point-in-time snapshot. The obligation will change when a child ages out, private school tuition changes, health insurance changes, or either parent's income changes materially (a 15% variance triggers a modification right under T.C.A. § 36-5-101(g)). A well-drafted MDA should anticipate these triggers.