Why value the whole job again every month instead of just this month's work?

Because measurement is never final until it is. Valuing cumulatively and deducting everything previously certified means an error in any earlier month corrects itself the moment it is spotted — the certificate simply comes out smaller, with no credit note, no adjustment line and no argument about which month it belonged to. Valuing month by month locks every mistake in place and forces a separate correction that somebody has to agree to, which on a difficult job is exactly the conversation nobody has.

What is the difference between the retention rate and the retention limit?

The rate is how fast retention accrues; the limit is where it stops. A common pairing is 5% withheld up to a maximum of 3% of the contract sum, which means retention accumulates for the first 60% of the job and then stops entirely. Applying the rate without the limit under-values every certificate for the back half of the contract — a 900,000 job at that pairing leaves about 9,200 uncollected on a single certificate near the end — and that is money owed, not money at risk.

Should materials on site be in the valuation at all?

In most standard forms yes, but conditionally: they must be on site, delivered at the right time rather than prematurely, adequately protected and insured. Note the direction of the ownership test, which is the opposite of the way it is often stated: employer ownership is a CONSEQUENCE of certification and payment, not a precondition of valuing the materials — title passes once the amount has been certified and paid. What does defeat a claim is the contractor not having good title to pass on, typically because a supplier's retention-of-title clause is still live, and ownership must have passed to the employer. Materials stored OFF site are usually excluded entirely unless the contract specifically allows them, and then only with a vesting certificate and often a bond. Keep the line separate and reduce it as each batch is built in — the value moves into the measured work at that point, and a batch left in both places is paid for twice, which is the sort of thing that gets found in a final account when there is no goodwill left to spend on it.

Can a certificate be negative?

Arithmetically yes, and it means more has been certified than the work now supports — usually because an earlier valuation over-measured, or because a deduction has landed that exceeds the month's progress. What happens next is a contract question rather than an arithmetic one: several standard forms carry a negative forward against the next certificate rather than creating a debt payable immediately. Check the payment provisions before issuing one, because getting that wrong turns a bookkeeping correction into a dispute.

Does this tell me when I will be paid?

No — it tells you what the certificate should come to. When the money arrives depends on the payment terms: the date the application is due, the date the certificate must be issued, and the final date for payment, all of which the contract sets and all of which are separate from the amount. The working capital panel inside My Project on this site takes those terms alongside a programme and shows what the lag costs while it runs — the peak of your own money in the job, and when the retention comes back — which is the other half of the same question.

Financial-Adjacent

Interim Payment Valuation Calculator (Certificate Due)

Net due on this month's interim valuation: gross value to date, retention against its limit, materials on site and earlier payments, in the right order.

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Market

Imperial · sales tax

Contract Sum

The original contract sum, before variations.

The retention cap is a percentage of THIS figure, which is why it is asked for even though the valuation is built from measured work. Whether agreed variations enlarge the sum the cap is taken on depends on the contract — most standard forms base it on the original sum, so that is what this uses.

Work Properly Executed To Date

Cumulative value of measured work completed, not this month's slice.

CUMULATIVE, not the increment — that is what makes the whole method self-correcting. If last month over-measured a floor slab, entering the true cumulative figure this month simply reduces what is due now, with no credit note and no argument. 'Properly executed' is doing real work in that phrase: defective work is not valued, and neither is work that has been done out of sequence in a way the contract does not accept.

Agreed Variations To Date

Cumulative value of variations agreed and executed. Omissions go in negative.

Only what has been AGREED and DONE. A variation instructed but not yet valued has no place in a certificate — it goes in the application as a notified sum and gets argued separately, and putting an optimistic figure here is the fastest way to have the whole certificate held up. An omission is a negative number, and omissions are routinely forgotten because nobody chases a credit.

Materials On Site, Not Yet Built In

Unfixed materials delivered and stored on site.

Payable in most standard forms where they are on site at the right time, properly protected and reasonably brought there. Title passes ON payment rather than before it — that is the direction, and getting it backwards costs money: a supplier's retention-of-title clause does NOT disqualify materials from an on-site valuation, and a contractor who drops the line because the supplier is unpaid has given away a certificate they were entitled to. Keep the line separate month to month: as each batch is built in it moves into the measured work, and a batch counted in both places is paid for twice. Materials stored OFF site are a different and far stricter test, usually excluded without a vesting agreement and a bond.

Retention Rate

Percent withheld from the cumulative gross valuation.

5% is the common rate on a main contract, often halving to 2.5% at practical completion and releasing entirely at the end of the defects liability period. It is applied to the CUMULATIVE gross figure, not to each month's increment — the two agree only while nothing is ever revalued downward.

Retention Limit

Maximum retention held, as a percent of the contract sum. Enter 0 for no limit.

The rate and the limit are two different numbers and both are in the contract: 5% withheld up to a total of 3% of the contract sum is the ordinary pairing. Once the limit is reached, no further retention comes off — which happens at 60% complete on those figures, and from there every certificate is larger than a naive 5% calculation says. Missing this under-values every application through the back half of a job, which is exactly when cash is tightest.

Total Previously Certified

Sum of all previous certificates, net of retention, before this one.

The NET figure — what was actually certified after retention — not the gross valuations those certificates were built from. Mixing the two is a common slip and it shows up as a certificate that looks roughly right but is out by the retention on every previous month at once.

Deductions and Contra Charges

Anything the contract lets the payer deduct from this certificate.

Liquidated damages where a completion date has passed, the cost of work the employer has had done by others after a notice, plant or attendance supplied and rechargeable, insurance excesses. Most standard forms require notice before a deduction is valid, and a deduction made without one is usually recoverable — so enter what has been properly notified rather than what somebody intends to withhold.

Net due on this certificate

$100,900

High confidence

Retention is still accruing at 5% and will stop at 27000, which on these figures is a cumulative gross of about 540000. Keep the materials-on-site line separate month to month: as each batch is built in it moves into the measured work, and a batch left in both places is paid for twice.

Gross valuation to date: $422,000
Retention held: $21,100
Valuation less retention: $400,900
Less previously certified: $300,000
Less deductions: $0
Progress against the adjusted sum: 45.67 %
Net due, unrounded: $100,900

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Standard forms of building contract (JCT, NEC, FIDIC and the AIA payment application) all value interim payments on the CUMULATIVE value of work properly executed to the valuation date, deduct retention from that cumulative figure, and then deduct the total previously certified — so an over- or under-measure in an earlier month self-corrects rather than compounding
Retention is commonly deducted at 5% of the cumulative gross valuation, LIMITED to a total of 3% of the contract sum; once that limit is reached no further retention is withheld, however much work follows
Materials and goods on site but not yet incorporated are payable in most standard forms where they are on site at the right time, adequately protected and reasonably brought there; title then passes TO the employer once the amount has been included in a certificate and paid. Materials stored OFF site are treated far more strictly and are commonly excluded entirely without a vesting agreement and a bond

Inputs used

Contract Sum: 900000
Work Properly Executed To Date: 380000
Agreed Variations To Date: 24000
Materials On Site, Not Yet Built In: 18000
Retention Rate: 5
Retention Limit: 3
Total Previously Certified: 300000
Deductions and Contra Charges: 0

Intermediate steps

Gross valuation to date: $422,000
Retention held: $21,100
Valuation less retention: $400,900
Less previously certified: $300,000
Less deductions: $0
Progress against the adjusted sum: 45.67 %
Net due, unrounded: $100,900

Final result$100,900

Confidence note: Retention is still accruing at 5% and will stop at 27000, which on these figures is a cumulative gross of about 540000. Keep the materials-on-site line separate month to month: as each batch is built in it moves into the measured work, and a batch left in both places is paid for twice.

What this calculation does not cover

The contract governs, not this page: the rate, the limit, what counts as properly executed and whether a deduction has been validly notified are all things it decides.
Sales tax is excluded on every line. It is added to the certified amount at the end, on whatever basis the contract and the jurisdiction set.
Assumes retention at one rate. Where a contract halves the rate at practical completion, run the two periods separately.
Off-site materials are not distinguished here; most standard forms exclude them without a vesting certificate and a bond, so they usually do not belong in the materials line at all.
No interest, financing charge or late-payment entitlement is calculated.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations3

Standard forms of building contract (JCT, NEC, FIDIC and the AIA payment application) all value interim payments on the CUMULATIVE value of work properly executed to the valuation date, deduct retention from that cumulative figure, and then deduct the total previously certified — so an over- or under-measure in an earlier month self-corrects rather than compounding
Retention is commonly deducted at 5% of the cumulative gross valuation, LIMITED to a total of 3% of the contract sum; once that limit is reached no further retention is withheld, however much work follows
Materials and goods on site but not yet incorporated are payable in most standard forms where they are on site at the right time, adequately protected and reasonably brought there; title then passes TO the employer once the amount has been included in a certificate and paid. Materials stored OFF site are treated far more strictly and are commonly excluded entirely without a vesting agreement and a bond

Which documents these citations point at

National Electrical Code (NFPA 70) (United States)Electrical installations — conductor sizing and protection, load calculation, wiring methods, grounding and working clearances.

A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.

Cite this page

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These guides cover the work this quantity is for.

How to calculate interim payment valuation (certificate due) in 9 steps

Contract SumThe original contract sum, before variations.
Work Properly Executed To DateCumulative value of measured work completed, not this month's slice.
Agreed Variations To DateCumulative value of variations agreed and executed. Omissions go in negative.
Materials On Site, Not Yet Built InUnfixed materials delivered and stored on site.
Retention RatePercent withheld from the cumulative gross valuation.
Retention LimitMaximum retention held, as a percent of the contract sum. Enter 0 for no limit.
Total Previously CertifiedSum of all previous certificates, net of retention, before this one.
Deductions and Contra ChargesAnything the contract lets the payer deduct from this certificate.
Net due on this certificateThe tool computes the net due on this certificate from those figures and shows the formula, its sources, and a confidence rating alongside it.

Net due on this certificate by contract sum

Page defaults, not your figures above.

Contract Sum	Net due on this certificate (currency)
100,000	119,000
200,000	116,000
500,000	107,000
1,000,000	100,900
2,000,000	100,900
5,000,000	100,900

Frequently asked questions

Why value the whole job again every month instead of just this month's work?: Because measurement is never final until it is. Valuing cumulatively and deducting everything previously certified means an error in any earlier month corrects itself the moment it is spotted — the certificate simply comes out smaller, with no credit note, no adjustment line and no argument about which month it belonged to. Valuing month by month locks every mistake in place and forces a separate correction that somebody has to agree to, which on a difficult job is exactly the conversation nobody has.
What is the difference between the retention rate and the retention limit?: The rate is how fast retention accrues; the limit is where it stops. A common pairing is 5% withheld up to a maximum of 3% of the contract sum, which means retention accumulates for the first 60% of the job and then stops entirely. Applying the rate without the limit under-values every certificate for the back half of the contract — a 900,000 job at that pairing leaves about 9,200 uncollected on a single certificate near the end — and that is money owed, not money at risk.
Should materials on site be in the valuation at all?: In most standard forms yes, but conditionally: they must be on site, delivered at the right time rather than prematurely, adequately protected and insured. Note the direction of the ownership test, which is the opposite of the way it is often stated: employer ownership is a CONSEQUENCE of certification and payment, not a precondition of valuing the materials — title passes once the amount has been certified and paid. What does defeat a claim is the contractor not having good title to pass on, typically because a supplier's retention-of-title clause is still live, and ownership must have passed to the employer. Materials stored OFF site are usually excluded entirely unless the contract specifically allows them, and then only with a vesting certificate and often a bond. Keep the line separate and reduce it as each batch is built in — the value moves into the measured work at that point, and a batch left in both places is paid for twice, which is the sort of thing that gets found in a final account when there is no goodwill left to spend on it.
Can a certificate be negative?: Arithmetically yes, and it means more has been certified than the work now supports — usually because an earlier valuation over-measured, or because a deduction has landed that exceeds the month's progress. What happens next is a contract question rather than an arithmetic one: several standard forms carry a negative forward against the next certificate rather than creating a debt payable immediately. Check the payment provisions before issuing one, because getting that wrong turns a bookkeeping correction into a dispute.
Does this tell me when I will be paid?: No — it tells you what the certificate should come to. When the money arrives depends on the payment terms: the date the application is due, the date the certificate must be issued, and the final date for payment, all of which the contract sets and all of which are separate from the amount. The working capital panel inside My Project on this site takes those terms alongside a programme and shows what the lag costs while it runs — the peak of your own money in the job, and when the retention comes back — which is the other half of the same question.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.