Two of the three ways to challenge a VA decision have a hard deadline: a Higher-Level Review and a Board appeal must be filed within one year of the date on your decision notice. Miss it and that door closes.
The third way, a Supplemental Claim, has no such bar. You can file one at any time. That sounds like the safe option, and it's where the expensive mistake lives.
File your Supplemental Claim within that same one year and your effective date reaches back to your original claim, or to the date your entitlement arose if that's later. File it after the year runs and the effective date resets to the later of the date entitlement arose or the day VA receives the new claim. Same evidence. Same grant. But the retroactive pay in between is simply gone. That stretch is often years.
Two narrow exceptions, because they invert the rule. If yours is a simultaneously contested claim — two claimants competing for the same benefit, or an apportionment dispute — the window is 60 days, not a year, and a Board appeal is the only route open to you. And a Supplemental Claim is not available after a denial of a request to revise a decision for clear and unmistakable error. If either might describe your case, do not rely on the one-year rule.
If there is a decision letter sitting on your kitchen table with a date on it, the date is the thing to look at right now.
38 C.F.R. § 3.2500(a)(1), (f), (g), (h)(1)–(2)