2.2 Revenue from contracts with customers
Key estimate: upfront fee revenue
Upfront fee revenue is recognised on a net basis of the historical percentage of ‘referred’ sales expected to become ‘financial’ and that do not trigger a ‘clawback’. These estimates are adjusted to actual percentages experienced at each reporting date. As such, the Group determines its revenue by estimating variable consideration and applying the constraint by utilising industry data and historical experience (refer to note 3.6 for further information).
Key estimate: trail commission revenue
The method of revenue recognition for trail commission revenue requires Directors and management to make certain estimates and assumptions based on industry data and historical experience of the Group. Refer to note 3.4 for details on trail commission revenue.
Recognition and measurement
Revenue represents the variable consideration estimated at the point in time when the Group has essentially completed its contracted services and constrained until it is highly probable that a significant revenue reversal in the amount of cumulative revenue recognised will not occur when the associated uncertainty with the variable consideration is subsequently resolved.
Upfront fees
When the Group refers a consumer to the product provider (and thereby satisfies its performance obligation), the Group is entitled to an upfront fee that is contingent upon the following events: (a) the referred sale becoming ‘financial’, which occurs upon new members joining a health fund, initiating a life insurance policy, obtaining general insurance products, mortgages, broadband or energy products via iSelect; and (b) whether a ‘clawback’ of the upfront fee is triggered. Upfront fees may trigger a ‘clawback’ of revenue in the event of early termination by customers as specified in individual product provider agreements. These contingencies are incorporated into the estimate of variable consideration (refer to key estimates).
Click-through fees
Click-through fees are recognised based on the contractual arrangement with the relevant product provider. This can occur at one of three points; either when an internet user clicks on a paying advertiser’s link, submits an application or a submitted application is approved.
Advertising and subscription fees
Revenue for contracted services, including advertising and subscription fees, are recognised based on the transaction price allocated to each key performance obligation. As a result, non-refundable revenue may be recognised across multiple periods until the performance obligation has been satisfied.
Trail commission revenue
Trail commissions are ongoing fees for customers referred to individual product providers or who have applied for mortgages via iSelect. Trail commission revenue represents commission earned calculated as a percentage of the value of the underlying policy relationship to the expected life and, in the case of mortgages, a proportion of the underlying value of the loan. The Group is entitled to receive trail commission without having to perform further services. On initial recognition, trail revenue and assets are recognised at expected value and subject to constraints.
Table:
 | CONSOLIDATED | 
 | 2019 $'000 | 2018 $'000
Upfront revenue |  | 
Upfront fees | 113,609 | 140,971
Click-through fees | 3,657 | 1,349
Advertising and subscription fees | 2,161 | 1,604
 | 119,427 | 143,924
Trail commission revenue | 34,732 | 33,007
Total revenue from contracts with customers | 154,159 | 176,931
Revenue related to performance obligations satisfied in previous years | 502 | 4,760


Question: What is the percentage change in upfront fees from 2018 to 2019?
Answer: -19.41
Calculation: (113,609-140,971)/140,971