In its Green Budget report issued in association with Barclays, the institute called for "more ambitious plans", saying the fresh cuts would have to come on top of the planned £57bn squeeze.
The think-tank has sought to reassure investors that the government debt arising out of the recession would be tackled.
Official figures show the UK economy is still struggling, with growth of just 0.1 per cent, far lower than earlier forecast.
The fiscal measures planned by Chancellor Alistair Darling would amount to a tightening of £57bn, which is 4.1 per cent of national income.
The IFS study said that though the Treasury should avoid "putting the recovery at undue risk", the Government should aim to tighten around 5 per cent of national income -- or £70bn -- over the next five years.
IFS director Robert Chote said it is "more important to show that you can last the course rather than be leading off the first bend."
The institute has also called for an independent body to oversee official forecasts for public finances.