Calculation to figure out spousal support?

Generally speaking if you have been financially dependant or interdependent upon your spouse for a significant period of time, then you would likely have an entitlement to spousal support upon separation.
If there are no children then under the Spousal Support Advisory Guidelines (SSAG) the formula is that you take the difference in your annual incomes and multiply that difference time the number of years of cohabitation times either 1.5% (low range), 1.75% (mid range) or 2% (high range) up to a maximum of 50% (at the 25 year cohabitation duration) and divide the result by 12 to get the monthly amount of support payable. So if his income was $75,000 and yours was $25,000, then the income differential would be $50,000 X 10 (years of cohabitation) X 1.75% (mid range) = $8750 per annum which divided by 12 = $729.16 per month as the mid range level of support. You can look up the SSAG calculator online to calculate the range of support payable.