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August swoon
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A slowing economy in China and hints at higher interest rates in the U.S. sent stocks into a tailspin in August. The rout trimmed retirement balances. But it also gave savers an opportune moment to convert 401(k) and IRA assets into Roth accounts, which they did in impressive numbers, new research shows.

Conversions to Roth IRAs are up 36% the year ending Sept. 30 and jumped a whopping 69% in August vs. the year-ago period, Fidelity Investments reports in its quarterly analysis of retirement accounts under its administration.

Converting to a Roth generally makes the most sense when asset prices have fallen. A traditional IRA is funded with pre-tax dollars and you pay tax upon taking distributions. A Roth is funded with after-tax dollars that then grow tax-free. When converting to a Roth, you owe immediate tax on the amount being converted. So by taking this step after asset prices have fallen—as opposed to while they were higher—you pay less tax.

Roth IRAs and Roth 401(k)s have been growing in popularity as savers worry about tax rates rising in the future and seek to diversify their tax-advantaged accounts. Plan sponsors have responded with expanded Roth options. More than half of Fidelity 401(k) plans now offer both a traditional pre-tax 401(k) as well as a Roth 401(k), up from about one-third three years ago. Some 70% of workers in a Fidelity 401(k) have access to a Roth option.

The Dow Jones Industrial Average dropped 11% in a week near the end of August, capping a 14% decline from the peak on May 19. The decline took the average 401(k) balance down to $84,400 at the end of September, compared to $91,100 at the end of June and $89,100 last year, Fidelity says. The average IRA balance fell to $88,700, compared to $96,300 in June and $92,100 last year.

The August turmoil clearly alarmed retirement savers. Fidelity handled 16 million online inquiries the last week of August and on Aug. 24 fielded 160,000 phone calls, one of the company’s busiest days on record. Not everyone stuck to their plan. But the vast majority did so; only 5% of 401(k) holders made changes to their asset mix in the third quarter and the contribution rate actually edged higher, Fidelity says. So most steady-Eddie investors ended up buying more shares at market lows, which is always a smart move.

It takes guts to stay the course while stocks are plummeting. But those who did so in August have been amply rewarded. Concerns over China’s growth and higher interest rates in the U.S. remain. But the panic has abated and the Dow has regained all of its August losses—and those who seized on the volatility to convert to a Roth account appear to have had impeccable timing.

Read next: Do These 5 Things Now If You Want to Retire in 5 Years