Former US president Donald Trump’ s corporate executives once boosted the estimated worth of his Trump Tower penthouse partly because of the value of his celebrity, according to trial testimony.

The value of the penthouse was allegedly boosted by $US20 million ($31 million).

Another $US100 million ($157 million) hike in the estimate was based on a single email from a real estate broker, who hadn’t commissioned an appraisal, didn’t inspect the triplex and was told it was three times its actual size.

From a witness stand, former Trump Organisation controller Jeffrey McConney shed light on Thursday on calculations central to Trump’s New York civil business fraud trial.

New York Attorney-General Letitia James’ lawsuit alleges the former president conspired with top executives to exaggerate his wealth and deceived lenders and others. Trump denies any wrongdoing.

In pre-trial testimony, the former president said that people who did business with him were given ample warning not to trust the statements, and that he never thought that the documents “would be taken very seriously”.

He described the financial statements as more a “compilation of properties” than a true representation of their value, saying some numbers were “guesstimates”.

But McConney’s testimony came with evidence that the documents were integral to some of Trump’s loan deals. In letters shown in the court, McConney told a bank that he was providing Trump’s 2015 and 2016 financial statements as required under the conditions of a loan for his Seven Springs estate north of New York City.

To figure the penthouse value, Trump executives combed through real estate listings, looking only for the highest-priced similar apartments, McConney testified.

And the $US100 million ($157 million) increase in 2012?

“I’m basing that on the email from Kevin,” McConney said, referring to real estate agent Kevin Sneddon. The broker had offered a quick estimate based on an asking price for a similar triplex in a Trump-owned building elsewhere in Manhattan – an apartment that ultimately sold for only 40 per cent of the asking price.

Protesters have been a continual presence outside former Donald Trump’s civil business fraud trial.

The next year, McConney tacked on another $US20 million ($31 million), upping the estimated value of Trump’s penthouse to $US200 million ($314 million). He said the change was based partly on a Trump real estate executive’s suggestion that the apartment’s celebrity connection warranted a higher price.

McConney also acknowledged making his own calculations, instead of relying on the numbers in a bank appraisal, to increase the stated worth of Trump’s Wall Street office building by $US227 million ($356 million).

Those and other asset valuations went onto Trump’s financial statements, which in turn went to banks, insurers and others. James calls that “persistent and repeated fraud.”

Trump says James, a Democrat, is just trying to damage his 2024 presidential campaign. He’s leading the Republican field.

Trump himself didn’t attend the proceedings Thursday, after choosing to be there — and avail himself of the news cameras waiting outside — for the three prior days.