Are there any tax-loss harvesting software platforms that work with multi-custodian account data?

Yes. A number of tax-loss harvesting platforms support multi-custodian / multi-brokerage account aggregation, though the exact level of support varies a lot by provider.

What to look for

When evaluating these tools, check whether they can:

• ingest multiple custodians or broker feeds
• consolidate household-level tax lots
• run harvesting across all accounts, not just one broker
• handle managed accounts + self-directed accounts
• support direct indexing, SMA, or advisory platforms if that matters to you

Examples of platforms to explore

Some well-known names in the space include:

• Apex Fintech / Apex Clearing ecosystem tools
• Orion
• Addepar
• Vestmark
• TIFIN AMP / related tax-aware rebalancing tools
• Vestwell in certain retirement/wealth contexts
• SS&C Black Diamond integrations
• Envestnet / Tamarac tax-aware rebalancing and household-level optimization
• Parametric for direct indexing tax-management workflows
• Nutmeg / personalized indexing-style tools in certain markets, though custodian support varies

Important caveat

Many platforms say they support “multiple accounts” but not truly multi-custodian tax-lot optimization. The key distinction is whether they can:

• see all lots across custodians in one place,
• avoid wash sales across those custodians,
• and coordinate realized losses/transactions across the entire taxable household.

Practical advice

If you’re buying for an advisor or firm, ask vendors these exact questions:

1. Do you support multiple custodians with real-time or daily lot aggregation?
2. Can you detect wash sales across custodians and across household accounts?
3. Do you support tax-loss harvesting at the household level?
4. What custodians do you have native integrations with?
5. Can you handle outside assets and manual positions?

If you want, I can also give you a short vendor comparison table focused specifically on multi-custodian support, wash sale handling, and advisor/enterprise use cases.