When to claim Social Security: PIA, full retirement age, and how Runway picks your best age
You can start Social Security in any month from 62 to 70, the amount you get depends on when you start, and you can't undo the choice. Runway's Basics step asks for two Social Security numbers — your PIA and your full retirement age — and the Social Security page then recommends claiming ages. This guide explains both terms and the arithmetic behind that recommendation.
What are PIA and full retirement age?
PIA (primary insurance amount) is the monthly benefit you'd receive if you start at your full retirement age (FRA) — the age at which Social Security pays your benefit with no reduction and no bonus. For anyone born in 1960 or later, the SSA sets full retirement age at 67 (SSA retirement planner). Every other number scales from the PIA, which is why Runway asks for it on the Basics step, one per person.
You can find your own figures on your Social Security Statement, which you can view by creating a free my Social Security account. Statements show estimates at several claiming ages; use the amount shown for your full retirement age as the PIA.
How much does claiming early or late change my benefit?
Claiming before full retirement age permanently reduces your monthly benefit; waiting past it permanently raises it, up to age 70. For someone with a $2,000 PIA and a full retirement age of 67, Runway's engine produces this schedule:
| Claim at | Monthly benefit | Share of PIA |
|---|---|---|
| 62 | $1,400 | 70% |
| 63 | $1,500 | 75% |
| 64 | $1,600 | 80% |
| 65 | $1,733 | 87% |
| 66 | $1,867 | 93% |
| 67 (full retirement age) | $2,000 | 100% |
| 68 | $2,160 | 108% |
| 69 | $2,320 | 116% |
| 70 | $2,480 | 124% |
The engine applies the standard rules: roughly 6⅔% off per year for the first three years before full retirement age and 5% per year beyond that, then an 8% bonus for each year you delay past it (delayed retirement credits stop at 70). The endpoints match the SSA's own schedule for people born in 1960 or later: 70% of PIA at 62, 100% at 67, 124% at 70. Amounts here are in today's dollars, so cost-of-living increases — which have their own wrinkle — don't appear.
So which claiming age is best?
There's no single right answer, but there is a clean way to compare ages: add up every payment you'd expect to receive, weight each year by the probability you're still alive then, and discount future dollars at 3% a year. Runway calls the result the expected lifetime value of a claiming age. For the same $2,000-PIA person, age 62 today:
| Claim at | Expected lifetime value |
|---|---|
| 62 | $285,924 |
| 65 | $293,843 |
| 67 | $296,984 |
| 68 | $299,344 |
| 69 | $299,457 |
| 70 | $297,499 |
Age 69 wins, but look at the shape: 68, 69 and 70 sit within $1,958 of each other, and 67 is only $2,473 below the top. Claiming at 62 is $13,533 below the best age. That flatness is the real message — once you're near the top, the difference between neighboring ages is smaller than the uncertainty in how long you'll live, so health, your other income, and whether you'd rather have more money early or more protection late matter as much as the optimizer's pick.
How does this change for a couple?
A couple's choices interact, because when one spouse dies the survivor keeps the larger of the two benefits. Runway searches every combination of claiming ages for both people. For a couple who are both 62, with PIAs of $2,400 (Pat) and $1,800 (Alex) and a full retirement age of 67:
| Pat claims at | Alex claims at | Expected lifetime value | Versus the best |
|---|---|---|---|
| 69 | 69 | $652,325 | best |
| 70 | 70 | $649,386 | −$2,939 |
| 67 | 67 | $644,457 | −$7,868 |
| 62 | 62 | $615,348 | −$36,977 |
| 70 | 62 | $572,058 | −$80,267 |
| 62 | 70 | $492,873 | −$159,452 |
The last two rows are the instructive ones. Having the higher earner claim at 62 while the lower earner waits to 70 is by far the worst combination in the table, because the larger benefit is the one the survivor inherits and claiming at 62 permanently shrinks it. When one spouse's benefit is much bigger, that spouse's delay is what protects the surviving spouse. (For the sample couple the app loads — Pat 65 and Alex 64 — the engine's best pair is 69 and 68.)
What does the recommendation leave out?
- Life expectancy is modeled, not looked up. Runway uses a Gompertz mortality curve calibrated to roughly match published U.S. life expectancy (about a 50% chance of reaching 85 for a 65-year-old). It isn't the SSA period life table. If you expect to live notably shorter or longer than average, the best age shifts earlier or later.
- A fixed 3% discount rate, and claiming ages in whole years. The SSA lets you claim in any month.
- Survivor benefits are simplified to "the survivor receives the larger of the two benefits."
- Taxes on benefits, working while claiming, and family benefits are handled elsewhere in the plan or not at all in the claiming-age comparison.
- It maximizes expected value, not worst-case protection. Delaying also works as insurance against a long life. Whether that insurance is worth a smaller early check is a judgment, not a calculation.
How do I use this in Runway?
- Enter each person's PIA and full retirement age on the Basics step (the ? beside each field explains it).
- Open the Social Security page (free) to see the recommended ages and how the options compare. Pro adds the full claim-age grid.
- In Explore Your Plan (Pro), override the claiming ages and watch the chance your money lasts respond — claiming earlier means drawing more from savings in the early years. That interaction is why the claiming age belongs in the spending question, not outside it.
See your own best claiming age. Enter your PIA and ages and compare every option — free to start, no credit card required.
Try the plannerHow were these numbers computed?
Every figure comes from Runway's planning engine. The single-person example is a $2,000 PIA, full retirement age 67, age 62 today. The couple example is both aged 62 with PIAs of $2,400 and $1,800 and full retirement age 67; it includes spousal top-ups and the simplified survivor rule above. Expected lifetime value uses the mortality curve and 3% discount rate described in the previous section, over a horizon to age 100. Results are rounded to the nearest dollar.