For anyone that is looking for the answer to my own question above, here is how I fixed it:
with st.form(key='columns_in_form'):
c1, c2, c3, c4 = st.columns(4)
with c1:
initialInvestment = st.text_input("Starting capital",value=500)
with c2:
monthlyContribution = st.text_input("Monthly contribution (Optional)",value=100)
with c3:
annualRate = st.text_input("Annual increase rate in percentage",value="15")
with c4:
investingTimeYears = st.text_input("Duration in years:",value=10)
submitButton = st.form_submit_button(label = 'Calculate')
This did the trick, one form with four inputs in four different columns:
