How to start a Commingled Expense Detector for Bookkeepers business: plan and growth
Bookkeepers see the same thing in every small-business client: owners move money to personal accounts and call it 'business expense', and staff pay personally and ask to be 'reimbursed' without receipts.
An owner can start “Commingled Expense Detector for Bookkeepers” from a complaint people already posted. The offer, in one line: Flag personal-vs-business mixing in client bank feeds and request receipts before month-end close. It is for bookkeepers and accountants. Charge a B2B subscription, and test a price between $50 and $199 a month. Begin in the United States. Buyers already talk about this in r/Bookkeeping. One thread gathered 108 votes and 161 replies across Sep 14, 2026 – Oct 14, 2026. Use that room to meet the first twenty buyers. Do not export it, and do not republish the posts. The idea, the evidence, and the market estimate on this page are free to read. Two paid prompts finish the job: one drafts the offer, the price, and a ninety-day calendar; the other drafts a month of conversations and proof. One credit unlocks both. A software specification is not on this site. When the company is the product itself, a single link further down opens the founder library.
How do you handle clients who pull cash to…r/Bookkeeping · Sep 14, 2026 – Oct 14, 2026 · 108 votes · 161 replies · Open the thread
Who would pay
Bookkeepers and accountants. Start in the United States, and charge a B2B subscription, testing a price between $50 and $199 a month.
The thread above is the public complaint this business can learn from. Verbatim quotes are not invented. Further sources, when a later report adds them, stay with the evidence.
What buyers use today
- QuickBooks rules
- Manual review
- Keeper
The offer, in our words
A bookkeeper tool that automatically detects commingling patterns in client bank statements and flags them for documentation requests before period close.
Score 3.85, Hot. Pain, willingness to pay, demand, and the gap in current options drive it. We are not scoring how fast you can code.
Market size
An estimate, built from the bottom up: real customer counts × a realistic price. It shows the size of the prize, not a forecast.
TAM Total addressable
$57.6M a year
48,000 offices · US bookkeeping and non-CPA accounting offices
SAM Serviceable
$22.8M a year
19,000 offices · offices on QuickBooks or Xero
SOM Obtainable in 3 years
$456K a year
380 offices · 2% of the reachable segment in three years
What that means
380 offices at $100/mo = $456K ARR
Medium confidence · estimated Oct 2026
How we estimated this
- Base: 47,700 US bookkeeping and non-CPA accounting offices.
- Has the problem: 100% (every bookkeeping office cleans up mixed expenses).
- Revenue per office: $1,200 per year ($99/mo).
- Reachable: 40% (offices on QuickBooks or Xero).
- Three-year capture: 2% of the reachable segment.
TAM is customers with the problem × revenue per customer. SAM is the part a new business can reach. SOM is a cautious three-year share of SAM. The bars use a log scale. A share marked “assume” is our judgment, not a measurement.
Source: US Census, County Business Patterns 2023 (NAICS 541219)
The business-plan prompt
The offer, the price, and a ninety-day calendar, written for an agent. 1 credit unlocks both prompts for this idea: this plan and the growth playbook below.
# Business plan prompt: Commingled Expense Detector for Bookkeepers You are writing a practical plan for one owner who will sell this as a business. Do not write a software specification, a venture memo, or a feature list. Use short sentences. Where a number is unknown, give a range and say what to measure. ## The business Working name: Commingled Expense Detector for Bookkeepers What the customer gets: Flag personal-vs-business mixing in client bank feeds and request receipts before month-end close. Who pays: Bookkeepers and accountants
Locked · the first lines are above
Unlock both prompts for this idea · 1 credit ($9.99)
One credit opens the business plan and the growth playbook together, for good. Credits work on both businessideastobuild.com and realstartupideas.com.
Sign in once with your Real Startup Ideas account; the same credits work on both sites.
The growth playbook
Thirty weekdays of conversations and proof. Not an ad plan. Included with the plan above, on the same credit.
# Growth prompt: Commingled Expense Detector for Bookkeepers You are planning thirty days of distribution for a business that already has an offer. The offer: Flag personal-vs-business mixing in client bank feeds and request receipts before month-end close. The buyer: bookkeepers and accountants. Price band: between $50 and $199 a month. Do not propose ads, a viral loop, or a rebrand. Propose conversations, proof, and a repeatable weekly rhythm. ## Starting point A public thread in r/Bookkeeping drew 108 votes and 161 replies. The pain, in the owner's words: Bookkeepers see the same thing in every small-business client: owners move money to personal accounts and call it 'business expense', and staff pay personally and ask to be 'reimbursed' without receipts.
Locked · the first lines are above
Unlock both prompts for this idea · 1 credit ($9.99)
One credit opens the business plan and the growth playbook together, for good. Credits work on both businessideastobuild.com and realstartupideas.com.
Sign in once with your Real Startup Ideas account; the same credits work on both sites.
Questions
How much money do I need to start?
Enough to talk to buyers and deliver the offer once. A service version can start with a written process and a way to take payment. A software version is a larger bet and is not required to test the price. The band to test is $50–199 a month.
How should I price it?
Test a price between $50 and $199 a month, charged as a B2B subscription. Raise it after three paid pilots, not before the first conversation.
Where do the first customers come from?
r/Bookkeeping is the clue. A related thread gathered 108 votes and 161 replies. Show up there, follow the room's rules, and ask for conversations. Do not scrape it.
Do I need to write code?
No. The prompts on this page draft a plan and a month of growth. Code is a later choice. The founder site linked once below is where the build document lives, if you want it.
A separate site sells the agent build document and can build the product. Get the build PRD
A two-week build starts at $10,000 on that site, after a $1,000 scoping fee.
Plans and growth playbooks
One credit opens both prompts for this business.
The idea, the evidence, and the market estimate stay free. The business plan and the thirty-day growth playbook for Commingled Expense Detector for Bookkeepers cost one credit, together, and stay unlocked.
Credits work on both businessideastobuild.com and realstartupideas.com. Sign in once with your Real Startup Ideas account; it is the same wallet.