Spreadsheet date math is the kind of problem that seems trivial until you are the one staring at a column of dates, a lookup table, and the sinking realization that your tool of choice treats "add three months" as a suggestion rather than a command. The user here is not asking for a workaround or a macro. They are asking for something simpler: a way to take a duration that lives in years, months, or weeks, pair it with a date, and get a correct answer without building a custom script or reconfiguring their entire workflow. The fact that this is hard in a modern spreadsheet is not a small gap. It is a fundamental friction point between how people think about time and how their software models it.
What stands out in this scenario is the second table. That is the quiet hero of the story. The user already did the hard thinking. They understood the data, mapped out the relationships, and built a lookup structure that should make the whole process clean and repeatable. The problem is not their logic. It is that the spreadsheet does not let them express the result of that lookup as a time duration in natural units. They are not asking for a calculator that handles one-off math. They are asking for a system that respects the structure they built, which is exactly what an AI-native tool should do. When the tool forces you to convert everything to days or to hardcode values, it is not simplifying the work. It is pushing the complexity back onto you.
The practical takeaway here is that this should be a solved problem. If you have a date in one cell and a duration in another, the software should understand what those units mean and apply them correctly. The user should not have to choose between a clunky formula that breaks on month boundaries and a manual entry that invites errors. This is not an edge case. It is the core of what a spreadsheet is supposed to do: let you model real-world scenarios without losing your mind. When a tool makes you fight for something as basic as "add three months to this date based on a lookup," it is not meeting you halfway. It is making you do the heavy lifting.
The solution is not to abandon spreadsheets or to learn more arcane functions. It is to expect better. If your current tool cannot handle this, that is not a limitation of your data or your skill. It is a limitation of the tool. And you should not have to accept it. The next time you hit this wall, ask yourself whether the problem is the math or the software. Because the math is straightforward. The software is what is holding you back.