Why We Built This

For thirty-five years, Tennessee has been quietly doing something remarkable, and almost nobody outside the family law bar has noticed.

In 1989, Congress passed the Family Support Act, which required every state to adopt presumptive child support guidelines. States had to pick a model. Most picked one of two: the percentage-of-obligor-income model, which is mathematically simple but ignores the custodial parent's economic contribution, or the Income Shares model, which is conceptually elegant but mechanically demanding. Tennessee picked Income Shares. Then Tennessee did something the other Income Shares states didn't always do: they actually built it out.

The result is the body of rules at Tenn. Comp. R. & Regs. Chapter 1240-02-04 — a fifty-page document that, read carefully, represents one of the most thoughtful pieces of family law in the country. It addresses gross income with specificity. It handles imputation. It builds a Self-Support Reserve to protect low-income obligors from being ordered to pay more than they can afford. It scales the basic obligation through a 2,815-row schedule that's been econometrically calibrated to actual household spending on children at different income levels. It handles parenting time with a variable multiplier formula that reflects the economic reality that an alternate residential parent with substantial time is bearing real expenses. It caps the schedule at $28,250/month combined AGI and then continues with a marginal-rate formula above that. It cross-references the statutory cap at Tenn. Code Ann. § 36-5-101(e)(1)(B) so that high-income cases get judicial review of the children's actual needs rather than automatic wealth transfer. It even folds in case law — Hugger v. Hugger, Nash v. Mulle, Smith v. Smith — that shapes how the statutory cap operates in practice.

Read together, it's a system. It tries to do justice to the actual variety of family situations. It has a place for the unemployed obligor and the surgeon obligor. It has a place for 80-day parenting and 182.5-day parenting and everything in between. It has a place for the stay-at-home parent and the two-physician couple and the one-million-dollar-earner whose ex still makes $300,000. It tries to give predictable, principled answers to all of them.

And then it fails to deliver on its own promise. Not because the rules are wrong. Because the rules are inaccessible.

The Spreadsheet Problem

If you go to the Tennessee Department of Human Services website right now and download the official Income Shares Worksheet, you'll get a 2.5MB Excel file. It's a .xlsm — macro-enabled. It has six tabs, dozens of named ranges, hundreds of cells, and a VBA macro layer that does the actual calculations. It's a heroic piece of work for what it is, but what it is, is a spreadsheet trying to do a database's job.

I know this because my brother downloaded it. His computer choked trying to open it. The error message was something to the effect of "too many formulas." He gave up.

He's not an outlier. The official worksheet runs only on certain versions of Excel. It requires macros enabled, which most enterprise IT departments disable by default. It has a separate Mac version and Windows version, and they don't behave identically. There's an iOS app, but it produces different outputs than the spreadsheets in some edge cases. The TN AOC has a web calculator too, but it doesn't generate court-ready outputs and it doesn't show its work.

So what happens in practice? The work falls to law firms. Attorneys and paralegals run the numbers themselves, manually, often in their own internal spreadsheets that were built years ago by someone who's since left the firm. The math gets done. The math gets done correctly more often than not. But the math gets done in private, behind the closed doors of one side's lawyer, and then the result gets presented to the other side as a position.

A position. Not a statement.

Here's the difference: a statement is "this is what the law says, this is what the math produces, this is what the order should be." A position is "this is what I'm going to argue for, and you're going to argue for something different, and we'll fight about it." Tennessee's rules were designed to produce statements. The way the rules are accessed produces positions.

This isn't anyone's fault. Lawyers have an ethical duty under Rule 1.3 of the Tennessee Rules of Professional Conduct to act with reasonable diligence in representing their client. They have a duty under Rule 1.1 of competence. In an adversarial system, when you're given an opaque, fragile, hard-to-verify calculation tool and a complex set of rules that reasonable people could interpret differently, your duty is to interpret them in your client's favor. That's the system working as designed. The problem isn't the lawyers. The problem is that the tools the lawyers are given turn statements into positions.

What Happens When Statements Become Positions

In high-income Tennessee divorce cases — which is most of the cases our firm handles — the practical result of the spreadsheet problem is that child support gets conflated with alimony.

I want to be careful here. I am not accusing anyone of anything. I'm describing a structural outcome of the system.

Here's how it happens. The Income Shares model in Tennessee, applied honestly, produces a number that's grounded in actual child-rearing economics and bounded by a statutory cap and a body of case law about the children's reasonable needs. For two high earners in a 50/50 custody arrangement, that number is often surprisingly modest. For a high earner with a moderate-earning ex in standard parenting, the number can exceed the statutory cap and trigger a burden-shift to the recipient parent.

But the recipient parent's lawyer, looking at a wealthy obligor and a client who is about to lose a substantial portion of the household standard of living, has a duty to argue for a higher number. The mechanism is available: deviation arguments under Rule .07. Extraordinary expenses. Educational expenses. The children's needs. The standard of living during the marriage. All legitimate, all in the rules, all subject to interpretation.

And on the other side, the obligor's lawyer, looking at the formula output and a client who is about to have a chunk of their income redirected, has a duty to argue for a lower number. The mechanisms are available: the statutory cap. The recipient parent's burden. Hugger and Smith. The children's actual needs versus the recipient parent's lifestyle preferences.

Both sides are doing their job. Both sides are interpreting an opaque system in their client's favor. And what happens in the middle, structurally and statistically, is that the dispute drifts. The recipient parent's lawyer pushes for a number that includes things the recipient parent would have received under alimony if alimony had been awarded — household maintenance, lifestyle preservation, a piece of the standard of living. The obligor's lawyer pushes back against any of that, and the resulting compromise number is somewhere in the middle.

That middle number isn't really child support anymore. It's child support plus a quiet, unofficial alimony component, hiding inside deviation arguments that no one can quite audit because the underlying calculation was never transparent in the first place.

Tennessee's legislature did not intend this. The statute is explicit: alimony is governed by Tenn. Code Ann. § 36-5-121, which has its own factors, its own analysis, its own appellate review. Child support is governed by § 36-5-101 and Chapter 1240-02-04, which have their own factors, their own analysis, their own review. The legislature kept them separate on purpose. The structural opacity of the calculation tool blurs the line between them in practice.

This isn't a Tennessee problem specifically. Other states that adopted Income Shares have seen the same pattern, and it's one of the things that scares states that haven't yet adopted Income Shares. They look at Tennessee, they see the conflation, and they conclude that Income Shares is too complicated to administer cleanly. So they stay with simpler models — like Mississippi's flat percentage of obligor income — that produce predictable results at the cost of nuance.

The Mississippi Tradeoff

Mississippi's child support statute fits on three pages. Miss. Code Ann. § 43-19-101 establishes a flat percentage: 14% of adjusted gross income for one child, 20% for two, 22% for three, 24% for four, 26% for five or more. That's the entire calculation engine. No schedule. No parenting time adjustment. No 50/50 cross-credit. No SSR. No above-cap formula.

Mississippi handles nuance differently. § 43-19-103 lists ten criteria — extraordinary medical expenses, the age of the child, the particular shared parental arrangement, total available assets, "any other adjustment which is needed to achieve an equitable result" — that allow the court to deviate from the flat percentage. Deviation is fully discretionary. The chancellor decides.

I'm a Mississippi-licensed attorney. I have great respect for the Mississippi chancery system and for the judges who serve in it. They take this work seriously, and they do their best to reach equitable results.

But Mississippi's system, by design, pushes the difficult work onto the judiciary at the time of the case. The chancellor has to absorb the facts, weigh the ten statutory factors, consider the totality of the circumstances, and exercise discretion. The result is whatever the chancellor concludes is equitable. Different chancellors reach different conclusions on similar facts. Different counties have different cultures. Predictability suffers.

Tennessee's system, by contrast, tries to do the hard work in advance, at the legislative level, by encoding the principles into rules that produce predictable outputs. When the rules are accessible, this works beautifully. Two parents at $65,000/month and $20,000/month with three children and 50/50 custody should produce the same support number whether they're in Memphis or Knoxville, whether their judge is conservative or liberal, whether their lawyers are aggressive or accommodating. The number is what the rules say it is.

The Mississippi tradeoff is: simpler statute, more judicial discretion, less predictability, lower administrative cost, but a wider range of outcomes for similarly-situated families.

The Tennessee tradeoff is: more complex statute, more predictability, less judicial discretion, higher administrative cost, but a narrower range of outcomes for similarly-situated families — if the administrative complexity is actually delivered to the users.

That "if" is the problem we set out to solve.

What We Built

We built a calculator. It runs at tncsg.tcblaw.org. It implements Tennessee's Income Shares model as defined in Chapter 1240-02-04 and § 36-5-101. It uses the verified BCSO schedule data from the official 2022 TN DHS worksheet. It applies the above-cap formula correctly. It engages the Self-Support Reserve when the obligor is in the shaded area. It applies the variable multiplier for parenting time adjustments. It handles the 50/50 cross-credit using the literal reading of Rule .04(7)(b)(2)(i). It flags the statutory presumptive cap under § 36-5-101(e)(1)(B) and explains the burden-shift to the recipient parent. It applies the Means-Tested Income zero-order rule. It handles private school as a discretionary deviation. It correctly distinguishes Special Expenses from Extraordinary Educational Expenses and applies the 7% threshold to the former.

It has eight verification tests covering every income zone and parenting arrangement. It cross-checks the math against the official TN DHS worksheet. It produces both an on-screen worksheet and a PDF output that mirrors the official AOC form.

It explains itself. There's a How It Works page that walks through the model in plain English, with five worked use cases covering single-earner, high-earner / moderate-earner, two-high-earners-with-disparity, two-high-earners-with-near-parity, and ultra-high-income scenarios. Each case shows the math, identifies which protections engage, and explains the strategic implications for both parents.

It is open source. The repository lives at github.com/tcbmem-png/csg_tcblaw. Every formula is annotated with its rule citation. Every calculation can be traced from input to output. Any attorney, any party, any judge, any contributor can audit the code, verify the math, and propose corrections.

It is not legal advice. It is a calculator. It produces the presumptive number that the Tennessee Income Shares model dictates given the inputs. What the parties do with that number — what they negotiate, what they file, what the court ultimately orders — is and remains a function of human judgment exercised in the specific context of the case.

But the number is the number. It is no longer a position. It is a statement.

Why This Matters

For thirty-five years, Tennessee's family law bar has been working with a system that's brilliant in design and broken in delivery. The legislature did good work. The rules do good work. The official worksheet does good work, when it works at all, for the people who can get it to open. The breakdown happens at the point where ordinary parties — parents trying to negotiate a parenting plan, parents trying to assess whether their existing order should be modified, parents trying to understand what to expect before they file — try to use the system without paying a lawyer to run the numbers in private.

We have made the system accessible. We have made it transparent. We have made it auditable. We have not changed the math. The math was already there.

What changes when the math is accessible is that the conversation between divorcing parents changes. Instead of "my lawyer says X and your lawyer says Y and we're $5,000 a month apart," the conversation becomes "we both put our incomes into the calculator, here's what the rules produce, here's what the protections do, here's where the discretion lives." That conversation is shorter. That conversation is cheaper. That conversation is more likely to settle. And the settlement is more likely to reflect what the legislature actually intended, rather than the gravitational pull of the adversarial process.

Lawyers don't lose work in this system. Lawyers gain time. The time that used to be spent running numbers in spreadsheets and arguing over the resulting outputs gets redirected to the work that actually requires legal judgment: the deviations, the imputation analyses, the parenting plan negotiations, the cases where the formula doesn't tell you what to do because the facts are unusual. That's the work lawyers should be doing. That's the work clients should be paying for. The math should never have been the bottleneck.

We are not arrogant about this. We did not invent the Income Shares model. We did not write the rules. We did not develop the case law. All we did was take what the Tennessee legislature, the Department of Human Services, and the appellate courts have spent three decades building, and translate it from a fragile spreadsheet into a calculator that any parent can use.

If it helps people, that's what it's for. If it helps lawyers, that's what it's for. If it helps other states see that the Income Shares model can be administered cleanly — without conflating child support with alimony, without inviting adversarial drift, without sacrificing predictability — that's what it's for too.

Tennessee got something right. We just made it visible.

A Word About What's Next

We're building the Mississippi version next, at mscsg.tcblaw.org. Mississippi's calculator will be simpler because Mississippi's statute is simpler, but it will be transparent in the same way. It will show the calculation. It will show the deviation factors. It will respect the chancellor's discretion by being explicit about where discretion lives and where it doesn't.

After Mississippi: Alabama, Arkansas, and possibly Louisiana. The same architecture, the same transparency, the same respect for what each state's legislature has decided about how child support should work in their state.

The goal is not to replace lawyers. The goal is not to replace courts. The goal is to make the math visible — the math that's already been done, decades ago, by legislators and rule-writers and judges who did good work that nobody can currently see.

Tennessee did the work. We're just turning on the lights.