would like to know how much will we get from bitcoin savings account in a bitcoin standard world
The long term rate of interest has tended to converge around 2 1/2%. This rate has been found by natural 'price discovery' over 100's of years, without the setting of rates which we take for granted nowadays.
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The long term rate is complicated by the fluctuations in inflation, which obviously affects the real interest rate drastically. Before fiat money, inflation was uncommon but began to appear in response to money issuers ie Sovereign Rulers , needing additional finance, and thus using their influence to debase currency. Possibly one could argue there was no need for an interest rate before the institutionalisation of money.