Standard said 98% of its remaining 318,000 mortgage endowment customers would face shortfalls if still using the plan to repay their mortgage, including 100,000 whose policies mature this year. It said those customers had seen the value of their policies increase by 7.9% last year, while the "heritage" with-profits fund made a return of 9.6%.
The 50,000 holders of Standard's with-profits bonds, along with holders of stakeholder pensions, made returns of around 15%, as their fund segments are backed by 60% to 67% equities whereas endowment holders are backed by only 40% equities.
The typical £50-a-month mortgage plan taken out over 25 years is now paying out £26,184, compared with £27,791 a year ago, £37,763 in 2008 and over £100,000 at its peak 13 years ago. Standard stresses that each policy has a "different time period" of returns.
The insurer, which demutualised in 2006, paid out a special dividend to shareholders last year and its shares are some 60% above their flotation price. A spokeswoman said: "With-profits customers received shares and if they had kept the shares they would have benefited.
"The with-profits fund is totally separate and ring-fenced from shareholder profits."
She said endowment maturities were now at their peak, adding: "We don't know how many people need the endowment to pay off their mortgage, some will have kept it going for the life cover, but we have been writing to people for quite a long time informing them about the shortfall."
The Financial Ombudsman Service reported a 43% uplift in complaints about mortgage endowments last year, but upheld only 21% of them compared with an average uphold rate of 49%.
Long-suffering holders of Standard's unitised plans, where bonuses have been slashed from 1.5% to 0.5% over the past three years, will welcome this year's reversal, with life plan bonuses going back up to 0.75% and pension bonuses to 1%.
The bonus rates on conventional life and pension policies are again unchanged at 0.25% to 0.35% while lucky holders of 3% and 4% guarantees continue to be subsidised by those without guarantees. With-profits bonds bonuses are again held at the relatively generous level of 2.5%.
The typical 20-year pension plan pay-out, on a £200 a month policy, also shows a rare uplift, from £77,703 to £78,669. That compares with a maturity of £92,735 in 2008. Standard said its 750,000 pension customers had enjoyed a real return of 12.6% last year.
Margaret Flaherty, Standard Life's with-profits communications manager, said: "With average returns on the fund of 8.6% we're pleased to say that customers will see a year-on-year increase in the value of their plan." Customers could check their plan values online as well as in annual statements.
Pat Connolly, certified financial planner at one of Scotland's biggest independent financial advisers Chase De Vere, said Standard had been able to maintain equity weightings of up to 68%, and strong equity performance in 2013 meant healthy fund returns. "This has allowed them to increase some annual bonus rates which is very positive and also increase payouts for 20-year pension policies.
"However, payouts on endowment policies have again been cut and overall returns remain much lower than they were five or six years ago ."
Mr Connolly, a sector analyst, added: "This announcement confirms that Standard Life remains an average, middle-of-the-road with-profits provider.
"While the outstanding equity returns of 2013 should help to buck the trend of lower with-profits bonuses and reduced payouts, which has been in place for over a decade, weaker investment returns in 2014 would probably mean this is just a temporary respite.
"Existing investors should take this opportunity to review their policies."