Generic invoicing software assumes a fee is one of two things: a flat number, or an hourly rate multiplied by hours logged. Neither describes how a meaningful share of financial advisor revenue actually gets billed. A large part of it is a percentage of assets under management, recalculated every cycle as the portfolio value moves — and that number has to be computed by the billing software, not typed in by hand from a rate card.
AUM fees are calculated, not entered
An hourly consultant's invoice starts from a number you already know: hours times rate. An AUM-based fee starts from a portfolio balance that changes daily, an annual rate, a billing frequency, and a valuation method — average daily balance over the period, or a single point-in-time snapshot. Two advisors charging the same nominal 1% can land on different dollar figures for the same client depending only on which valuation method their software applies.
A client holds an $850,000 portfolio, billed at 1% annually, in arrears, quarterly.
Point-in-time (quarter-end balance): $850,000 × 1% ÷ 4 = $2,125 for the quarter.
Average daily balance (the portfolio averaged $830,000 over the quarter due to market movement): $830,000 × 1% ÷ 4 = $2,075 — a different number, same rate, same client, purely because of how the software measured the balance.
Flat planning fees ride alongside the AUM fee, not instead of it
Plenty of advisors also charge a flat planning fee — commonly $1,500–$3,000 — for a standalone financial plan or ongoing service that sits outside asset management. On its own, that fee behaves exactly like a generalist consultant's retainer: fixed, recurring, easy to invoice. The complication is that it usually doesn't stand alone — it needs to appear on the same household statement as the AUM fee, not as a separate, disconnected bill the client has to reconcile themselves.
Hybrid models need one invoice, two calculations
A hybrid fee structure charges both: a reduced AUM percentage plus a flat retainer, billed together.
Same $850,000 portfolio, billed quarterly: 0.85% AUM fee = $1,806, plus a $500/quarter flat planning retainer. Total debit: $2,306, shown as two separate, disclosed components on one household invoice — not a single unexplained number.
That last part matters beyond bookkeeping. Advisory clients — and often the compliance rules an advisor operates under — expect a fee breakdown, not a lump sum. Software built for flat consulting fees has no concept of a second, variable component riding on the same bill.
Advance vs. arrears changes what "paid" even means
AUM fees are commonly billed either in advance (based on the prior period's ending balance, covering the upcoming quarter) or in arrears (based on the quarter just completed). The difference isn't academic: if a client terminates mid-quarter under an advance-billing arrangement, the advisor typically owes a prorated refund for the unearned remainder of the period. Under arrears billing, no refund calculation is needed — the fee only ever covered work already done. Generic invoicing tools have no field for billing basis at all, let alone the proration math a mid-cycle cancellation requires.
What this means for choosing software
Billing software built for a fee-based advisory practice needs to do four things a flat-fee or hourly invoicing tool doesn't: calculate AUM fees automatically from account balances rather than requiring manual math, support tiered or breakpoint fee schedules, combine multiple fee types — AUM and flat — onto a single disclosed household invoice, and handle advance-versus-arrears billing including mid-cycle refund proration. None of that is generic billing hygiene; it's specific to how fee-based advisory revenue actually works.
The flat planning-fee or retainer portion of that revenue, on the other hand, doesn't need anything AUM-specific — it just needs to go out clean and dated like any other consulting invoice. The free Consulting Invoice Generator handles that side well, even if the AUM calculation itself still lives in a purpose-built billing system.