Google Ads Conversions Over Time
Not everyone buys on their first visit to your site, and
Here’s one example of how much the conversion went up by when given enough time for all the conversion data to come in.

This will vary depending on how far in the past you are looking at conversions, your conversion window and your conversion path length.
But as a rough guide, if you are looking at ‘last week’, conversion value is probably at least 5% lower than it will look once you have waited for all the conversion data to come in.