Here’s a simplified example of this works: Let’s say you’re a four person software dev startup. Everybody is making, say, $125K to get by. That’s $500K in salary expense which normally you can write off as expenses against revenue/funding. For this example, let’s say somehow you also generated $500K in revenue/funding, i.e. you just broke even.
Currently, you would (of course) owe zero taxes. Under the new tax rules, you couldn’t write off those R&D salaries as expenses, only amortize them over 5 years. That is, your salary expenses for this year is only ~ $100K, and this you made a $400K ‘profit’ (!!) on which you owe taxes ($100K).