Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Actual gross margin after creep
59.7%
Effective hourly rate earned
$154
Unbilled overage hours
12.0
Cost of the overage
$744
Fee increase to restore target margin
-$836
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
Got your number — what next?
Pick one, it takes 20 secondsHow to use this
- 1Enter monthly retainer fee ($).
- 2Enter contracted hours per month (hrs).
- 3Enter actual hours delivered (hrs).
- 4Enter loaded delivery cost per hour ($/hr).
- 5Enter target gross margin (%).
- 6Read your actual gross margin after creep on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
A retainer priced at 40 hours a month that quietly consumes 52 has not lost 12 hours — it has lost the entire margin on those hours plus the opportunity cost of what that capacity could have billed elsewhere. This calculator compares contracted hours to actual delivered hours, prices the overage at your loaded cost, and shows the retainer's effective hourly rate and margin after creep. It also shows the fee increase required to restore your original margin, which is the number to bring to the renewal conversation. Scope creep is the most common cause of a 55%-margin proposal turning into a 20%-margin account without anyone noticing until the year-end review.
Worked example
Using the values the calculator loads with:
Inputs
- Monthly retainer fee: 8000 $
- Contracted hours per month: 40 hrs
- Actual hours delivered: 52 hrs
- Loaded delivery cost per hour: 62 $/hr
- Target gross margin: 55 %
Results
- Actual gross margin after creep: 59.7%
- Effective hourly rate earned: $153.85
- Unbilled overage hours: 12
- Cost of the overage: $744.00
- Fee increase to restore target margin: -$835.56
What each field means
Inputs
- Monthly retainer fee ($)
- The monthly retainer fee used in the calculation, measured in $. Starts at 8000 $ so you have a working example on load.
- Contracted hours per month (hrs)
- The contracted hours per month used in the calculation, measured in hrs. Starts at 40 hrs so you have a working example on load.
- Actual hours delivered (hrs)
- The actual hours delivered used in the calculation, measured in hrs. Starts at 52 hrs so you have a working example on load.
- Loaded delivery cost per hour ($/hr)
- The loaded delivery cost per hour used in the calculation, measured in $/hr. Starts at 62 $/hr so you have a working example on load.
- Target gross margin (%)
- The target gross margin used in the calculation, measured in %. Starts at 55 % so you have a working example on load. Accepted range: 5–90 %.
Results
- Actual gross margin after creep
- Returned as a percentage and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Effective hourly rate earned
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Unbilled overage hours
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cost of the overage
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Fee increase to restore target margin
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Is some scope creep normal?
A 5-10% variance against contracted hours is normal and usually not worth policing. Past 20% you are running a different engagement than the one you priced, and the fix is a scope conversation, not more efficiency.
Should I bill overage or raise the retainer?
Raise the retainer when the overage is structural and recurring — clients hate surprise invoices far more than a predictable higher fee. Bill overage only for genuinely one-off requests, and make the mechanism explicit in the contract before the first one happens.
How do I track actual hours if the team hates timesheets?
Track at the account and week level rather than the task and minute level. Weekly per-account hour totals are accurate enough to catch a 30% overage and cheap enough that people actually record them.
What if the effective rate is still above my cost?
Then the account is profitable but underpriced, which is a slower problem than a loss-making one. Compare the effective rate to your blended target rate — the gap, multiplied by annual hours, is what the account is costing you in opportunity.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Agency Blended Hourly Rate Calculator
Find the single hourly rate a mixed delivery team has to bill to hit target margin.
Client Concentration Risk Calculator
Measure how exposed your revenue is to losing your biggest account.
Project Effective Hourly Rate Calculator
Divide the real project fee by every hour it consumed, including sales and admin.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Retainer Scope Creep Cost Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/retainer-scope-creep
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/retainer-scope-creep" target="_blank" rel="noopener">Retainer Scope Creep Cost Calculator — RevenueLab</a> (2026).</p>
Source: [Retainer Scope Creep Cost Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/retainer-scope-creep) (2026).