When a business needs stronger budgeting, cash forecasting, or financial decision support, it can hire internally, engage an outside provider, or combine the two. A useful build-versus-buy model compares the cost of meeting the same requirements over the same period. It should explain capacity and service differences before presenting a cheaper option.
This article is part of our guide to cash flow forecasting and financial planning.
The financial example below separates one-time costs from recurring costs and shows the correct break-even formula. It is a hypothetical decision model, not salary research, a provider quote, or a promise that either staffing approach will produce a particular result.
Define the work before comparing prices
List the decisions and recurring deliverables the finance function must support. Examples include a monthly operating forecast, weekly cash updates, budget variance analysis, lender reporting, and models for a major purchase or expansion. Specify the data needed, report due dates, meeting frequency, response times, and authority to approve or execute transactions.
Also identify bookkeeping, payroll, financial-statement preparation, tax returns, and specialized advice. An internal employee may need outside specialists; an outsourced engagement may include some operational accounting or may only provide advisory work. Neither an employee title nor a provider’s CFO label establishes the scope.
OpenStax’s make-or-buy analysis applies the comparison of internal and external alternatives to both goods and services. Here, that decision framework is applied to a finance function; it does not establish a standard CFO salary, fee, or staffing horizon.
Compare productive capacity, not just billed hours or employment status. Account for experience, specialist coverage, administration, leave, ramp-up, and the ability to meet deadlines when workload peaks. A full-time employee and a small monthly advisory package may both be useful, but they are not equivalent options unless each can meet the actual requirements.
Separate costs that differ from costs that continue either way
Use future costs and benefits that change with the choice. OpenStax’s relevant-cost guidance distinguishes differential costs, unavoidable costs, and sunk costs. Money already spent on an earlier search does not become a new cash requirement merely because management changes direction.
For example, existing bookkeeping fees that remain identical under both options can be disclosed as a common cost. Include them in the full finance budget, but they do not explain the difference between the alternatives. If one option changes that scope or fee, include the incremental amount.
Keep three views separate: the decision’s future outlays, the accounting expense pattern, and the economic value of resources such as owner time. An equipment purchase can be an upfront cash outlay while its book expense is recognized over time. Do not add both the purchase price and its depreciation as separate cash costs in the same model.
Build a complete internal-cost estimate
For an employee, identify salary or hourly pay, any applicable overtime and bonuses, employer payroll taxes, employer-paid benefits, recruiting, onboarding, training, technology, workspace, and necessary specialist support. Identify when each cost begins and whether it changes with headcount, compensation, or workload.
Employer payroll taxes are not one universal percentage of salary. Social Security has an annual wage base; regular Medicare does not. FUTA and Florida reemployment tax have their own wage bases, rates, and adjustments. Additional Medicare withholding is employee-only. Use the employee’s taxable compensation and the rules for the relevant year, checking IRS Publication 15 and the employer’s Florida reemployment-tax rate.
Gross wages already include employee withholding. In a cash schedule, the net paycheck plus employee amounts remitted reconcile to gross pay; add employer taxes separately. Do not add employee withholding on top of gross wages as another employer expense.
Annual salary normally already pays the employee during included paid leave. Do not add the same paid time off again as a separate salary cost. Instead, reflect reduced productive capacity and any actual additional coverage cost. Include turnover, recruiting delays, temporary coverage, and any applicable separation obligations in scenarios.
Price the outside scope just as carefully
Obtain the recurring fee, onboarding charge, minimum commitment, included hours and skills, overage rates, price increases, travel costs, technology charges, and exit terms. Determine who supplies licenses, integrations, equipment, data cleanup, and coverage when the primary adviser is absent.
Outsourcing does not necessarily reduce the owner’s oversight time or eliminate additional specialists. The business still needs someone to provide records, approve assumptions, review deliverables, and make decisions. Estimate that work separately for each option.
A contract with a genuine outside provider is different from misclassifying an individual employee as a contractor. Determine the actual working relationship and applicable worker-classification rules; paying against an invoice or using a contractor label does not settle that question.
The cumulative-cost equations and correct crossing point
Let B0 be the build option’s one-time cost and Bm its recurring monthly cost. Let U0 and Um be the corresponding buy costs. For a simplified model with constant recurring costs and no other changes:
- Build total at month t = B0 + Bm × t
- Buy total at month t = U0 + Um × t
Set the totals equal and solve:
Break-even months = (B0 − U0) ÷ (Um − Bm)
The denominator is buy monthly cost minus build monthly cost. Reversing that subtraction while keeping the same numerator gives the wrong sign. Also, do not amortize the upfront costs into Bm and Um and then include B0 and U0 again.
If the monthly costs are equal but upfront costs differ, the initial cost difference persists and there is no crossing. If both upfront and monthly costs match, every period ties. If only upfront costs match, the options tie at time zero and the lower recurring-cost option is cheaper thereafter.
A negative calculated time does not provide a future break-even point. A positive crossing beyond the chosen horizon means there is no crossing within that horizon, not that the lines never cross. For actual monthly payments, check cumulative totals at payment dates rather than treating a fractional month as a guaranteed cash recovery date.
A filled hypothetical comparison
Assume both options can provide the same mix of skills and at least 100 productive finance hours per month, with the same reporting deadlines, access expectations, and required coverage. The internal employee’s broader paid time includes administration and leave; the outside service commits equivalent required capacity. These are assumptions to verify, not typical staffing or market-price claims.
Use a twelve-month initial decision horizon. The following is an undiscounted screening model using level monthly recurring-cost estimates. It is not a dated payroll cash forecast. Payroll tax caps, deposit dates, benefit payments, fee billing, and actual start dates must be scheduled separately before using the result to plan bank balances.
| Cost input | Build internally | Buy outside support |
|---|---|---|
| One-time recruiting, setup, equipment, and onboarding | $18,000 | $3,000 |
| Monthly salary or service fee | $10,000 salary | $14,000 service fee |
| Monthly employer-tax planning estimate | $800 | Provider’s employment costs are within this hypothetical service fee |
| Monthly employer-paid benefits | $900 | Within this hypothetical service fee |
| Monthly technology and other incremental support | $300 | $500 |
| Total recurring monthly estimate | $12,000 | $14,500 |
The $800 employer-tax line is a modeling estimate, not a statutory rate or a claim that taxes are paid evenly each month. Replace it with employee-specific calculations and actual timing. Both options retain the same existing bookkeeping and tax-return services, which are common costs outside this incremental comparison. Assume both are ready when the recurring period starts, with no price changes, exit charges, or terminal recoveries in this simple model. Test departures from those assumptions separately.
Build therefore costs $18,000 + $12,000 × t, while buy costs $3,000 + $14,500 × t. The crossing is ($18,000 − $3,000) ÷ ($14,500 − $12,000) = 6 months.
| Horizon | Build | Buy | Difference |
|---|---|---|---|
| 3 months | $54,000 | $46,500 | Buy is $7,500 lower |
| 6 months | $90,000 | $90,000 | Equal |
| 12 months | $162,000 | $177,000 | Build is $15,000 lower |
| 24 months | $306,000 | $351,000 | Build is $45,000 lower if assumptions remain unchanged |
At twelve months, the build option has the lower modeled cost but requires $15,000 more upfront. Whether the business can fund that initial difference is a cash question. Whether both options actually meet the required work is a capacity and quality question. The cost result alone answers neither.
Test how a changed assumption changes the decision
If internal recurring costs rise to $14,000 while the buy option remains $14,500, the monthly difference narrows to $500. The crossing moves to $15,000 ÷ $500 = 30 months. At month 24, build costs $354,000 and buy costs $351,000, so buy is still $3,000 lower within that horizon. Both reach $438,000 at month 30.
This result does not support a universal three- or five-year planning rule. Choose a horizon consistent with the expected workload, contract duration, staffing commitment, and useful life of systems, then test a shorter and longer period. A temporary six-month project and a permanent finance function can require different analyses.
Also test a later start, slower ramp-up, a departing employee, fee escalation, additional specialist work, and increased demand. Model the downside condition separately from management’s response so the benefit of a proposed action remains visible.
Move from the screening model to dated cash flows
Place recruiting payments, equipment purchases, net payroll, withholding remittances, employer taxes, benefits, vendor invoices, and termination payments on their actual expected dates. Include deposits, minimum fees, prepaid services, and any recoverable amounts at the end of the horizon. Avoid treating an average monthly cost as an exact monthly bank withdrawal.
For a longer or uneven comparison, calculate present values using a stated discount rate and cash-flow dates. Include supported tax effects at their expected timing rather than assuming that every outlay is immediately deductible. If service quality or capacity changes revenue or other costs, model those incremental effects explicitly instead of inventing a standard return on CFO support.
Show owner time separately. Five hours per month valued at $150 per hour represents $750 of assumed opportunity cost. It becomes a cash saving only if a payment actually disappears, or a separately supported cash benefit occurs. Do not count the same reclaimed time once as avoided cost and again as new profit without reconciling the assumptions.
For related guidance, our article on Budgeting Versus Forecasting walks through this in “Budgeting vs. Forecasting: Why Growing Businesses Need Both.”
Evaluate delivery and make the choice reviewable
For an internal role, confirm candidate capability, management support, recruiting lead time, access needs, and coverage. For a provider, request a proposed scope, sample deliverables, named responsibilities, response commitments, technology requirements, data-handling practices, and transition terms. Verify claims about credentials, security, and past results rather than treating marketing text as evidence.
A hybrid arrangement may combine internal accounting with occasional specialist planning, or outside support during a search. Price the handoffs and temporary duplication; do not assume a combination automatically costs less.
Use a practical sequence: define requirements, obtain comparable estimates, complete the cost and cash schedules, test capacity and downside scenarios, approve the scope and spending, and review actual results after an agreed operating period. Assign an owner and a target date to each step, including a date to revisit actual cost, capacity, and service quality.
If you want assistance reviewing the accounting and tax assumptions, contact CPA Firm South Florida’s fractional CFO team with the proposed role or service scope, cost estimates, current financial records, and planning horizon. Confirm the specific advisory work available and its fee; tax-preparation pricing is not a substitute for a quote for finance leadership or modeling services.
Frequently asked questions
What is the correct break-even formula?
With build upfront cost B0 and recurring monthly cost Bm, and buy upfront cost U0 and recurring monthly cost Um, cumulative costs are B0 + Bm × t and U0 + Um × t. If monthly costs differ, equality occurs at t = (B0 − U0) ÷ (Um − Bm). Check whether the result is nonnegative and relevant to the decision horizon.
Should recruiting or onboarding costs also be included in the monthly total?
Keep one-time costs separate in the cumulative-cost model. If you allocate them across months for a budget presentation, label that view and do not add the same upfront amount again when calculating total cost.
Does outsourcing always cost less than hiring?
No. The result depends on equivalent capacity, skills, scope, timing, fees, employer costs, and additional support. A lower upfront commitment can still produce a higher cumulative cost over a longer period.
Are bookkeeping and tax services automatically included in CFO support?
No. The engagement may include some of those tasks or may require separate providers. Identify the responsible person, deliverables, and price for each function instead of relying on the CFO title.
Is owner time a cash saving?
Owner time has an opportunity cost, but hours multiplied by an assumed value are not automatically cash saved. Show the time estimate separately unless the choice actually changes a payment or produces a supported incremental cash benefit.