Many of us--well, those of us with the wherewithal--are inclined to help out our grown kids in the here and now, rather than have them wait till our last will and testament is read. The down payment on a car or a house; the tab for day care for a grandchild--these are some of the things we may offer to help with--by gift or loan--and that give us a measure of pleasure to underwrite.
But what if it's not us offering the assist but them asking for an "advance" on the money we'll be leaving them? Does it matter what the ask is for? Does their asking, rather than our offering, put a different cast on the "feel good" moment? Are they presumptuous in their expectations?
It's complicated. A woman who wrote to Social Qs for advice on whether or not to ask her elderly parents for an "advance" to make it easier for her to buy a house, be able to underwrite family gatherings and otherwise "enjoy some of it while they're alive." The letter writer also noted that her parents had willingly paid for the education of her sister's children and that an "advance" would more or less even the financial-legacy scales.
Philip Galanes advice to the daughter in question is one we might take into account if such a request comes our way.
If you are sure that [your parents] are still competent to make this decision and can afford it, ask for a loan. Let them decide whether to make it a gift. And drop the tit-for-tat with your sister over her children’s education. That help was given at another time and probably long planned.
My biggest reservation here is that many parents I know would go without to help their children (even deep into adulthood). If that sounds like yours, stick with your original plan to pay for the house yourself. There comes a time to put our parents first, after years of the reverse arrangement.