Some 200,000 investors in with profits bonds and mortgage endowments with mutual insurer LV= are in line for an average bonus of £50.
This is the first time the mutual, previously known as Liverpool Victoria, has paid out a dividend of this type since its formation in 1843.
It says it has been made possible by its 'substantial growth' in the past few years.
The bonus, which amounts to £10m, will be paid into the mutual's giant with-profits fund on September 1.
Investors will get the money when their plan matures or when they cash in.
It equates to a boost of just 0.5% for each member.
But the firm says it hopes to be able to issue a bonus of 1% each year in future, if all goes well.
It aims to provide members with another £50 boost on average by the end of the financial year next April. This could make a big difference to savers in the longer term.
Without the bonus, a £25,000 investment in a with-profits bond would be worth £45,900 in ten years.
With a 1% annual bonus it would be worth £50,700 — more than 10% more.
This assumes annual investment growth of 5.75%.
Savers have £330bn in with profits plans, including bonds, endowments and pensions.