You billed 1,800 hours last year and still felt behind. Now three AI tools for lawyers promise to fix that — CoCounsel, Harvey AI, and Spellbook — and every comparison you’ve found lists features side by side without answering the question that actually matters.
At your billing rate, does this tool make money or burn it?
A solo attorney at $175/hour who spends $1,200/month on Harvey AI needs to save roughly 7 billable hours every month just to break even. Most won’t. Here’s the math for three billing rates and three tools — then which one (if any) makes financial sense for your practice.
Your Billing Rate Determines Everything
Forget features for a moment. Here’s what each tool costs and how many hours you need to recover before it pays for itself.
| Monthly Cost | Break Even at $150/hr | Break Even at $250/hr | Break Even at $400/hr | |
|---|---|---|---|---|
| CoCounsel | ~$225 | 1.5 hrs | ~1 hr | ~0.6 hrs |
| Spellbook | ~$200 | ~1.3 hrs | ~0.8 hrs | 0.5 hrs |
| Harvey AI | $1,200+/user | 8+ hrs | ~5 hrs | 3 hrs |
CoCounsel and Spellbook break even fast at any billing rate. Harvey’s unit economics are a different story — Gong, Chorus, and Clari face similar ROI math for sales teams, where unit economics also vary by team size and call volume. And that’s before the 20-seat minimum, which means your firm is committing $24,000/month at the floor.
Hidden costs make this worse. CoCounsel’s deepest research features require an existing Westlaw or Practical Law subscription. Harvey locks you into minimum commitment lengths. Spellbook’s pricing is the most straightforward of the three.
But breakeven alone doesn’t tell you which hours each tool actually saves. That depends on what kind of law you practice.
Three Tools, Three Different Lawyers
Stop comparing these as competitors. They dominate different practice areas, and picking the wrong one means paying for capabilities you’ll never use. If you’ve seen how different AI tools solve different problems in other fields, the same principle applies here.
CoCounsel (Thomson Reuters) is the research tool. Built for litigation, complex regulatory work, and M&A due diligence. Its Westlaw integration pulls from verified legal databases — not the open web — which matters when your cite needs to hold up in court. Expect 4–8 hours saved monthly on legal research and case analysis. The catch: a fragmented workflow split between a Word add-in and a separate portal. Two interfaces means more friction, and friction kills adoption.
Spellbook is the contract tool. Corporate, IP, transactional work — anything where you’re reviewing or drafting agreements. It lives inside Microsoft Word, which is why attorneys actually use it. No new interface to learn, no portal to switch to. Expect 5–10 hours saved monthly on contract review and drafting. The limitation: narrower scope. Don’t buy Spellbook expecting it to handle complex litigation research. That’s not what it does.
Harvey AI is the enterprise tool. Deepest reasoning on multi-step analysis across practice areas — but it requires 50+ seats, $1,200+ per user per month, and IT onboarding. For 95% of solo attorneys and small firms, Harvey is financially irrational. The math doesn’t work unless you’re spreading cost across a large team billing at $400+/hour.
Here’s the decision in plain terms:
- Spend 20+ hours/month on legal research → CoCounsel
- Spend 20+ hours/month on contracts → Spellbook
- Have 50+ attorneys and cross-practice complexity → Harvey
- None of the above → you may not need a dedicated legal AI tool yet
That narrows it. But there’s a cost these breakeven tables don’t show — the time you’ll still spend checking the AI’s work.
The Accuracy Tax You’re Still Paying
Harvey scored 94.8% accuracy on document Q&A in the VLAIR benchmark study. CoCounsel hit 89.6%. Those numbers sound high until you translate them to practice.
94.8% means roughly 1 in 20 answers contains an error. On initial research triage, that’s acceptable. On cite-checking or clause identification, that’s a malpractice risk.
The practical rule: AI handles first-pass triage and drafting, you review final output. Which means your “hours saved” calculation needs a haircut — budget 15–20% of saved time back for verification. If CoCounsel saves you 6 hours of research, plan to spend about an hour confirming what it found. AI spreadsheet tools show the same pattern — the verification tax isn’t unique to legal AI.
Where AI works without you hovering: initial research summaries, contract clause flagging, document organization. Where it doesn’t: final cite-checking, novel legal arguments, jurisdiction-specific nuance.
This is the accuracy tax. Legal AI doesn’t eliminate review hours — it restructures them. You spend less time finding information and more time verifying it. Net savings are real but smaller than vendor marketing implies.
Which brings us back to the original question.
The Bottom Line by Billing Rate
You came here to find out if legal AI makes or loses you money. Here it is in three lines.
Solo attorneys ($150–200/hr): CoCounsel if research-heavy, Spellbook if contract-focused. Both break even in under 2 hours of saved work per month — easily achievable. For a broader solo founder AI stack covering ROI-driven tool selection across roles, not just legal work, see our breakdown. Skip Harvey entirely.
Small firms ($250–400/hr): Same tool choice, faster payback. If your practice spans both research and contracts, running both tools still costs less than a single Harvey seat.
Enterprise ($400+/hr, 50+ seats): Harvey becomes rational here. The reasoning depth justifies the cost when amortized across a large team with complex, cross-practice needs.
One honest caveat: if your current workflow handles 30+ billable hours per week without bottlenecks, you may not need any of these yet. The worst ROI is paying for a tool your team never opens. That’s not a knock on the technology — it’s a reminder that the best legal AI tool is the one that actually fits the hours you’re already losing.