Will my money last?

A retirement projection: one return, one inflation rate, your cashflows by age, all in today's dollars. It answers whether the plan funds to the end, how much you could spend, how early you could stop, and what you would need to save or earn if it does not. The same engine runs inside Kaight, our AI planner, now in private beta.

Worked example: a 40-year-old with the median 401(k) balance for ages 35–44 ($35,537), earning $70,252 and saving 12.1% a year (the average total contribution rate, the employee's and the employer's together, so the employer field stays blank), who retires at 65 and spends what the average household over 65 spends ($61,432 a year), with the average Social Security retirement benefit ($23,712 a year from 67). The stress test replays the reference mix on its index layer (S&P 500 and intermediate Treasuries, history from 1962). Change any number below and run it again.

Sources

Vanguard, How America Saves 2025, median participant balance age 35–44; BLS usual weekly earnings, full-time workers age 35–44, 2025 Q2 median ($1,351 × 52); Vanguard, How America Saves 2025, average total contribution rate (employee + employer); BLS Consumer Expenditures 2024, average spending of households whose reference person is 65 or older ($61,432); SSA, average monthly benefit of retired workers, 2025 ($1,976 × 12), from the full retirement age of 67.

Hypothetical: a projection in today's dollars at an assumed return, checked against past market data, with an assumed flat tax on pre-tax withdrawals. Not a forecast, not advice.

At a 3.9% real return (6.5% assumed, 2.5% inflation), this plan runs out at age 76.

Based on: age 40, retiring at 65, $35,537 saved, $61,432 a year in retirement

Spending that lasts

$43,000 a year

Earliest retirement

Age 73

Savings at retirement

$459,180

Over history

0 of 105 lasted

The projection lasts to 95 with any one of these figures in place of yours: a savings rate of 25.0% (12.1% entered), a retirement age of 73, or spending of $43,000 a year. Replayed with the reference mix (index layer) over every start month since January 1962 (from today, 56 years), 0 of 105 complete paths lasted to 95. The worst, starting January 1962, ran out at 76.

The projection assumes 3.9% real a year. Over the same years, the replayed paths earned a median of 4.6% real, and 105 of 105 beat the assumption. That is why most replayed paths last longer than the projection. History check: the reference mix (index layer) fell short of the assumed 3.9% real in 22% of its 25-year windows before retirement and 12% of its 31-year windows in retirement.

Change the numbers

You and your savings

Current age

401(k), 403(b), traditional IRA (pre-tax)

$35,537

Roth IRA or Roth 401(k)

Brokerage, savings and cash (taxable)

Enter by account

Each account's type and value. Its funds are optional (a portfolio review reads them), as TICKER:percent lists summing to 100. For a fund the site does not know, add its expense ratio and class: FUNDX:[email protected]%us_stock (classes: us_stock, intl_stock, em_stock, us_bond, intl_bond, tips, cash, gold, commodities, reit, balanced, other).

Name Type Value Funds (optional) Gain %

Gain %: unrealized gain, taxable accounts only

Income and saving

Earned income, a year

$70,252

Income by age (optional)

Savings rate, % of income

Employer contribution, % of pay

Social Security, from your statement

$23,712

Pension

Add income or an expense

Each item's type, amount and years. From and to are ages, or calendar years (1900 or more); a blank "to" is one year for one-time income or an expense, and the plan's end for the rest. "Rises with inflation" is an amount in today's dollars; "fixed" is the amount as paid, which loses value with inflation (an annuity, usually). Spending changes apply from retirement on. A partner's Social Security: their birth year and their statement's amount, from the age they would claim (62 to 70; 67 if blank), to the "to" you give, both in their ages (a stand-in for the first death); no survivor benefit, no filing status.

Name Type Amount From To Rises with inflation? Expected or hoped for Partner's birth year Quoted at age A year or a month

Your retirement goal

Retire at

Plan to age

Spending in retirement, a year

$61,432

Assumptions

Return

Inflation, % a year

Tax on pre-tax withdrawals, %

Return from

Label

Stress test

Replays the plan's cashflows over every historical start month of a portfolio, in real terms: from retirement (accumulation keeps the assumed return) or from today (contributions ride the history too). Leave the portfolio blank for the projection alone.

Portfolio

From retirement (optional)

Replay from

Extended history

Use validated backfills and synthetics (what these are)

One person, spending after an assumed flat tax on pre-tax withdrawals, Social Security as you enter it, in today's dollars. Deterministic projection at one real return (3.9%/yr) with no variability. Not advice.

Projection

Funded?

No — runs out at 76

Savings at retirement

$459,180

Left at plan end

Initial withdrawal rate

15.2%

Real return used

3.9%

Max spending that funds

$43,000

Earliest retirement age

Savings rate needed

25.0%

Return needed

8.9%

Social Security from 67: $23,712 a year in today's dollars.

Taxes: 12% on pre-tax withdrawals, an assumption. At 0%: runs out at 78; at 20%: runs out at 75.

New saving is split across your savings in proportion to their balances by type (all to pre-tax when there are none).

Not modelled: tax brackets, required minimum distributions, Roth conversions, early-withdrawal penalties, and tax on gains or on Social Security. Savings of unknown type, and an old link's total, are taxed as pre-tax.

Year by year (today's dollars)

Year by year, in today's dollars
Age	Earned	Saved	Social Security	Pension	Other	Withdrawn	Of it, tax	Growth	Balance
40	$70,252	$8,500	$0	$0	$0	$0	$0	$1,387	$45,424
41	$70,252	$8,500	$0	$0	$0	$0	$0	$1,773	$55,697
42	$70,252	$8,500	$0	$0	$0	$0	$0	$2,174	$66,372
43	$70,252	$8,500	$0	$0	$0	$0	$0	$2,590	$77,462
44	$70,252	$8,500	$0	$0	$0	$0	$0	$3,023	$88,986
45	$70,252	$8,500	$0	$0	$0	$0	$0	$3,473	$100,959
46	$70,252	$8,500	$0	$0	$0	$0	$0	$3,940	$113,399
47	$70,252	$8,500	$0	$0	$0	$0	$0	$4,425	$126,325
48	$70,252	$8,500	$0	$0	$0	$0	$0	$4,930	$139,755
49	$70,252	$8,500	$0	$0	$0	$0	$0	$5,454	$153,709
50	$70,252	$8,500	$0	$0	$0	$0	$0	$5,998	$168,208
51	$70,252	$8,500	$0	$0	$0	$0	$0	$6,564	$183,273
52	$70,252	$8,500	$0	$0	$0	$0	$0	$7,152	$198,926
53	$70,252	$8,500	$0	$0	$0	$0	$0	$7,763	$215,189
54	$70,252	$8,500	$0	$0	$0	$0	$0	$8,398	$232,087
55	$70,252	$8,500	$0	$0	$0	$0	$0	$9,057	$249,645
56	$70,252	$8,500	$0	$0	$0	$0	$0	$9,742	$267,887
57	$70,252	$8,500	$0	$0	$0	$0	$0	$10,454	$286,842
58	$70,252	$8,500	$0	$0	$0	$0	$0	$11,194	$306,536
59	$70,252	$8,500	$0	$0	$0	$0	$0	$11,962	$326,999
60	$70,252	$8,500	$0	$0	$0	$0	$0	$12,761	$348,261
61	$70,252	$8,500	$0	$0	$0	$0	$0	$13,591	$370,352
62	$70,252	$8,500	$0	$0	$0	$0	$0	$14,453	$393,305
63	$70,252	$8,500	$0	$0	$0	$0	$0	$15,348	$417,154
64	$70,252	$8,500	$0	$0	$0	$0	$0	$16,279	$441,934
65	$0	$0	$0	$0	$0	$69,809	$8,377	$17,246	$389,371
66	$0	$0	$0	$0	$0	$69,809	$8,377	$15,195	$334,757
67	$0	$0	$23,712	$0	$0	$42,864	$5,144	$13,064	$304,957
68	$0	$0	$23,712	$0	$0	$42,864	$5,144	$11,901	$273,994
69	$0	$0	$23,712	$0	$0	$42,864	$5,144	$10,692	$241,823
70	$0	$0	$23,712	$0	$0	$42,864	$5,144	$9,437	$208,396
71	$0	$0	$23,712	$0	$0	$42,864	$5,144	$8,133	$173,665
72	$0	$0	$23,712	$0	$0	$42,864	$5,144	$6,777	$137,578
73	$0	$0	$23,712	$0	$0	$42,864	$5,144	$5,369	$100,084
74	$0	$0	$23,712	$0	$0	$42,864	$5,144	$3,906	$61,126
75	$0	$0	$23,712	$0	$0	$42,864	$5,144	$2,385	$20,648
76	$0	$0	$23,712	$0	$0	$21,453	$2,574	$806	$0
77	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
78	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
79	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
80	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
81	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
82	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
83	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
84	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
85	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
86	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
87	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
88	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
89	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
90	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
91	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
92	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
93	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
94	$0	$0	$23,712	$0	$0	$0	$0	$0	$0
95	$0	$0	$23,712	$0	$0	$0	$0	$0	$0

Stress test

Reference mix (index layer): VOO 60%, VGIT 40% · real returns 1962-01-31 to 2026-09-30 (bound by VGIT), deflated by CPI · replay from today (age 40, contributions and income phases ride the history) to 95 (56 years). Chosen by rule: the history holds 105 complete windows of the full path. Replay start by rule: from today while in accumulation when the history holds at least 25 complete windows of the full path; otherwise from retirement. Extended history on for VOO, VGIT (how).

Before the numbers: overlapping start months from one history are not independent trials; the count says how many, not how likely. Hypothetical, with an assumed flat tax on pre-tax withdrawals, not a forecast.

Start dates survived

0 of 105 complete

Success rate

0.0%

Worst start

1962-01-31 → out at 76

Median left at plan end

Assumed-return plan

out at 76 at 3.9% real

Start months tried

765 (105 complete)

Start dates that ran out (first 12 of 129)

Start dates that ran out
Start	Out at age	Years replayed	Window
1962-01-31	76	56	complete
1962-03-31	76	56	complete
1962-02-28	77	56	complete
1962-04-30	77	56	complete
1962-05-31	78	56	complete
1962-06-30	78	56	complete
1962-07-31	78	56	complete
1962-08-31	78	56	complete
1962-09-30	78	56	complete
1962-10-31	78	56	complete
1962-11-30	78	56	complete
1962-12-31	78	56	complete

Return reality check

Before the numbers: History of overlapping windows from one past, not a forecast: the percentiles say how often an N-year stretch delivered at least a given real return, never how likely the next one is. Reference mix: three-fund reaches 1992 (ex-US leg 1990); for windows before that use us_large / treas_int.

Assumed return 6.5% nominal = 3.902% real after 2.5% inflation. Horizons from the plan: 25 years to retirement, 31 years in retirement.

Real returns over the plan's horizons
Portfolio	Phase	Years	Windows	10th pct	Median	90th pct	Windows below assumption
Reference mix (index layer)	accumulation	25	477	2.86%	5.85%	7.10%	22.0%
Reference mix (index layer)	retirement	31	405	3.78%	5.74%	6.57%	11.6%
Reference mix (accumulation)	accumulation	25	114	3.31%	4.64%	5.28%	36.0%
Reference mix (retirement)	retirement	31	42	3.67%	3.81%	4.07%	71.4%

Real annualised returns of every complete window (start months 1962-01-31 to 2026-09-30, bound by VGIT, VTI). "Windows below assumption" is the share of windows that delivered less than the real return assumed for that phase; rows with fewer than 10 windows are thin; extended history is on.

Will my money last?

Result

You and your savings

Income and saving

Your retirement goal

Assumptions

Stress test

Projection

Stress test

Start dates that ran out (first 12 of 129)

Return reality check