Women who choose to leave the workforce or work part-time after having children could be forfeiting between $58,000 and $318,000 in retirement savings, research by NZIER has revealed.

The economic consultancy was charged with looking at the key drivers behind the 20 per cent gap between men and women's average KiwiSaver balances by state-owned KiwiSaver provider Kiwi Wealth.

It found labour force participation, the pay equity gap, career gaps and changes because of motherhood and low confidence and knowledge of the retirement savings scheme were behind the gap.

Christina Leung, principal economist at NZIER, said it wanted to quantify the effect of each driver and come up with policy solutions that could help ease the shortfalls.

"We know there is a gap but the extent of it was quite important for us to put a value on each of those drivers so that we are aware... and know which of the policy interventions would get the most bang for your buck."

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