SaaS magic number calculator
How much new ARR each dollar of sales and marketing buys, and whether you should be spending more or less. See the formula, change the inputs and save your results.
On this page 6 sections
The short answer
SaaS magic number uses arr at the end of this quarter, arr at the end of last quarter, sales and marketing spend last quarter to estimate magic number. Change the example inputs to your own figures. The result is a planning calculation, not an industry benchmark or a prediction.
Key points before you start
Use this tool alongside the saas metrics guide. How much new ARR each dollar of sales and marketing buys, and whether you should be spending more or less.
Your numbers
Defaults are illustrative inputs, not industry benchmarks. Use one consistent reporting period.
Results
Editable CSV worksheet
Save your marketing measurement plan
Keep a worksheet for your inputs, assumptions and next actions. You can also print the calculation directly from your browser.
Which inputs do you need?
| Input | Example value | What to check |
|---|---|---|
| ARR at the end of this quarter | 5,400,000 | Use the value from the same reporting period as the other inputs. |
| ARR at the end of last quarter | 4,900,000 | Use the value from the same reporting period as the other inputs. |
| Sales and marketing spend last quarter | 1,150,000 | Use the value from the same reporting period as the other inputs. |
Before entering numbers, choose the unit of analysis. An account, a user and a paying subscription are different objects. Counting users in one field and accounts in another can produce a precise answer to the wrong question. Record the start and end dates beside your source export so another person can reproduce your work.
What formulas does the calculator use?
Magic number
magic = sm > 0 ? (arrq - arrprev) / sm : NaNThis output is expressed as a ratio.
Net new ARR added
added = arrq - arrprevThis output is expressed as currency in the same units as the inputs.
Cost per dollar of new ARR
costper = (arrq - arrprev) > 0 ? sm / (arrq - arrprev) : NaNThis output is expressed as currency in the same units as the inputs.
Percent fields use whole percentages: enter 5 for five percent. The formula divides by 100 where a decimal rate is needed. Values in the formulas correspond to the labelled inputs above; earlier outputs can be used by later formulas.
Worked example
The defaults are a constructed scenario, not results from a named company or survey. With the example inputs above, the calculation produces:
| Output | Example result |
|---|---|
| Magic number | 0.43 |
| Net new ARR added | 500,000 |
| Cost per dollar of new ARR | 2.3 |
Change one assumption at a time and watch the main result. Then test a conservative case by reducing the expected benefit or increasing the associated cost. If a decision works only at the most optimistic settings, investigate the uncertain input before committing the budget.
How should you interpret the result?
A formula describes the assumptions entered into it. It cannot establish that a channel caused a sale, that historical retention will continue, or that a projected cost is achievable. Compare the output with your own previous cohorts before using a broad market comparison.
For a management review, save the result together with the source date, segment, owner and planned action. Recalculate when the underlying input changes. Keep a separate copy of the original scenario so the team can explain the difference between the plan and the observed outcome.
Continue the analysis
Use the metrics guide to align definitions, browse all calculators for adjacent calculations, and keep a measurement worksheet beside the model. The pricing hub and growth hub cover decisions that often change these inputs.
Apply saas magic number calculator in a working review
Record the source and unit of every input before using the result. Change one assumption at a time to understand which inputs matter most. Keep outputs that describe money, time and percentages distinct, and preserve undefined cases rather than converting them into plausible-looking zeroes.
For this topic, involve the metric owner and the source-system owner and work from metric dictionary, source records and cohort definition. The relevant unit is a consistent account, user, event or revenue cohort. State the question the review should resolve before choosing a chart, an asset or a tool. If participants disagree about the unit or scope, resolve that disagreement before combining their evidence.
Evidence to prepare
Write the numerator, denominator, unit, period, source and exclusions before interpreting the number. Separate observed data from assumptions and forecasts. A metric can be calculated correctly while still answering the wrong business question.
| Review field | What to record |
|---|---|
| Topic | SaaS magic number calculator |
| Decision | The specific action this explanation should help you choose |
| Working evidence | metric dictionary, source records and cohort definition |
| Unit and scope | a consistent account, user, event or revenue cohort |
| Responsible people | metric owner and the source-system owner |
| Remaining uncertainty | The missing fact that could change the decision |
Two situations that can change the interpretation
When CAC mixes new and existing customers
Dividing this month’s acquisition spend by the entire installed base produces a number that does not describe customer acquisition cost.
Use this check: Check the cost scope, new-customer definition and acquisition cohort timing. Costs and conversions must cover comparable periods or cohorts.
The focused diagnostic guide provides the correction process and a working evidence sheet.
When a conversion report mixes events and people
Five form submissions by one person are five events, but they are not five unique converted visitors.
Use this check: Document the counting unit at each step and inspect repeated-event behavior. Do not silently deduplicate events that represent legitimate separate transactions.
The focused diagnostic guide provides the correction process and a working evidence sheet.
Record the decision and the limit
Twenty activated accounts divided by eighty eligible accounts is 25%. Dividing the same twenty accounts by two hundred individual signups produces 10%, but it mixes units. Both inputs can be real while the second ratio is unsuitable for an account-activation claim.
Keep the conclusion beside the evidence that supports it. Record what the team will do, who owns the next action and which event or date will trigger a review. If the underlying definition, audience or product behavior changes, revisit the conclusion rather than assuming the old result still applies. A clear limit is useful information; it tells the next reader where additional investigation is required.
Use the complete topic collection for related methods and the category field guides when the product’s buying situation or implementation requirements change how the method should be applied.
A reproducible sensitivity exercise
The saas magic number calculator tool provides a related numerical exercise. Its current default inputs are constructed examples, not industry observations. Under those defaults, the output labelled Magic number is 0.43 in the tool’s displayed units. The table changes one input at a time and leaves the others at their defaults.
| Input changed | Default input | Alternative input | Magic number after change |
|---|---|---|---|
| ARR at the end of this quarter | 5,400,000 | 6,480,000 | 1.37 |
| ARR at the end of last quarter | 4,900,000 | 5,880,000 | -0.42 |
| Sales and marketing spend last quarter | 1,150,000 | 1,380,000 | 0.36 |
The alternative inputs are sensitivity cases, not recommended targets. A result marked not defined means the proposed combination does not satisfy the model or produces an undefined ratio. Keep that state visible. If the output changes sharply after a small input change, investigate the uncertain input before using the model to justify a larger commitment.
Compare the model’s scope with the concept on this page. The calculator may represent one particular application rather than every use of the term. Record the reporting period, currency where relevant, and the source of the real values you enter.
Editable CSV worksheet
Save your marketing measurement plan
Keep a worksheet for your inputs, assumptions and next actions. You can also print the calculation directly from your browser.
Frequently asked questions
How does this saas magic number calculator work?
It evaluates the formulas shown on this page in your browser. How much new ARR each dollar of sales and marketing buys, and whether you should be spending more or less. Inputs are not sent to a calculation server.
Are the default values SaaS industry benchmarks?
No. They are example inputs chosen to demonstrate the calculation. Replace them with your billing, CRM or finance records before making a decision.
Why does a result show n/a?
The calculation is undefined or an input is outside its allowed range. Check for an empty field, a zero denominator or an impossible percentage before interpreting the result.
Can I save or share my calculation?
Use Print or save results to create a local PDF with your browser. Review the inputs before sharing and remove confidential customer or company information.
The saas-marketing.net editorial team Research and editorial
We research, write and maintain every page on this site. The library explains marketing decisions through practical frameworks, explicit assumptions and references. Corrections can be requested through the contact page.
Published September 17, 2026. Last updated .