A 45-day window tends to show up in situations with a bit more room to breathe than a two-week deadline but that still need a firm end date — closing on a home purchase, a mortgage rate lock, a permit review period, or a promotional 0% financing offer that expires after a set number of days. Because it spans a month and a half, it’s also long enough that the answer almost always lands in a different month than it started, and sometimes crosses two month boundaries at once.
Working it out just means counting forward 45 individual calendar days from today, letting the tally spill from one month into the next (and the next, if needed) based on how many days each month actually has. As an example, if today were September 20th, 45 days forward would first use up the 10 remaining days of September, then all 31 days of October, leaving 4 days left over — landing on November 4th. Notice that the specific date you land on depends on exactly which months fall in that stretch, since a 45-day run through October and November covers different ground than one through, say, February and March.
That’s the main reason it’s worth calculating rather than estimating “about six and a half weeks” by eye — the exact landing date shifts depending on the months involved, and a contract deadline or rate-lock expiration doesn’t leave much margin for a rough guess.